First set of new device support, cleanups and features for IIO in the 5.9 cycle

Some new devices, but particularly good this time is the core rework coming
from Alexandru. Some of this has been in Analog's tree a long time, but other
parts are motivated by closing down common mistakes in new drivers.

Changes since first try at this pull request:
* Add missed patch to actually remove iio_priv_to_dev and as a result
  also drop a few ingenic patches that need to be updated to take this
  into account.
* Fix an ordering issue int he pollfunc attach in the core rework.

New device support
* qcom pmic7 adc
  - New driver using common qcom-vadc library. Some associated cleanups and
    refactors.
* invensense icm42600
  - New driver supporting icm42600, icm42602, icm42605 and icm42622 via i2c
    or spi.  These are all 6 axis IMUs with gyro and accelerometers.
    Driver supports buffered modes using the hardware fifo and interpolation
    for accurate timestamps.
* sensirion scd30
  - New driver for this carbon dioxide sensor including i2c and serial
    interfaces + bindings.

Features
* ak8975
  - Add reset gpio support.
* bma400
  - Support SPI.
* bmc150
  - Document and add support for bmc156b and bmm150b, tidy up _magn endings.
* bmi160
  - Regulator and mount matrix support.
* mxc4005
  - Add ID for mxc6655
* rockchip-saradc
  - Triggered buffer support.

DT bindings
* qcom spmi-vadc converted to yaml + pmic7 bindings
* ak8975 tidy up and convert to yaml + add reset-gpio binding
* ingenic-adc -convert to yaml.

Core rework all carried through by Alexandru Ardelean.
* Assign parent device in the core rather than every driver. A few devices
  need to provide specific non standard parents, so there is support for
  overriding.
* Start to take parts of struct iio_dev opaque to the drivers.
  This will be a long term job, but should reduce the number of drivers
  we get that use parts that are currently only 'internal' by documentation.
* Move attach and detach of pollfunc to the core.  Every triggered buffer
  using driver had to do the same thing, so lets do it in the core.  The
  hard part here was getting all the drivers into canonical form so there
  would be no functional changes in this final patch.  That's taken quite
  a lot of work over last couple of cycles!

Cleanups and minor fixes.
* docs
  - Improve IIO_CONCENTRATION channel type description in ABI docs.
  - Drop doubled word cases.
  - Http to Https conversion.
* core
  - Make iio_device_get_drvdata take a const struct iio_dev * avoiding some
    nasty casts.
* ADCs
  - Drop lots of users of of_match_ptr macro, includes of mod_devicetable.h
    and CONFIG_OF protections.  These prevent use of ACPI PRP0001 with these
    drivers and get coppied into lots of new drivers.
* ad5380
  - Constify iio_chan_spec_ext_info
* ad5592r
  - Constify iio_chan_spec_ext_info
  - Avoid use of iio_priv_to_dev (precursor to taking parts of iio_dev opaque)
* ad8366
  - Make gpio optional as doesn't matter if its there or not.
* adis16480
  - Use irq types instead of the flags.
* atlas-ezo-sensor
  - Minimize scope of ret variable.
* at91-adc
  - Add COMPILE_TEST dependency to driver to improve build coverage.
  - Avoid use of iio_priv_to_dev (precursor to taking parts of iio_dev opaque)
* at91-sama5d2
  - Avoid use of iio_priv_to_dev (precursor to taking parts of iio_dev opaque)
  - Drop Ludovic as a co-maintaienr.
* cros_ec
  - Reapply the range after resume.
  - Add a read only frequency entry for legacy version.
  - Typo fixes
* hts221
  - Avoid use of iio_priv_to_dev (precursor to taking parts of iio_dev opaque)
* inv_mpu
  - Drop double check on ACPI companion device.
* iqs621
  - Avoid use of iio_priv_to_dev (precursor to taking parts of iio_dev opaque)
* iqs624
  - Avoid use of iio_priv_to_dev (precursor to taking parts of iio_dev opaque)
* max11100
  - Constify iio_chan_spec
* mmc35240
  - Constify reg_default
* rockchip-saradc
  - Move to managed allocators for everything in probe.
  - Use more distinctive prefix for channel macros.
* stk3310
  - Constify regmap_config.
* stm32-adc
  - Avoid use of iio_priv_to_dev (precursor to taking parts of iio_dev opaque)
* stm32-dfsdm-adc
  - Avoid use of iio_priv_to_dev (precursor to taking parts of iio_dev opaque)
* ti-am335x
  - Use managed allocations where straight forward in probe function.
* tsl2563
  - Avoid use of iio_priv_to_dev (precursor to taking parts of iio_dev opaque)
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