First set of new device support, features and cleanup for IIO in the 5.1 cycle

A number of interesting new devices supported plus a good set of staging
cleanup including one graduation and one drop.

New device support
* ad56886
  - Add support for AD5674R/AD5679R with some minor driver changes to support
    more channels.
* ad7768
  - New driver and dt bindings for this 24 bit ADC.
* max44009
  - New driver and dt bindings for this ambient light sensor.
* mpu6050
  - Support the ICM 20602 IMU. Minor tweaks due to slightly different
    register map.
* NPCM adc
  - New driver and dt bindings for this BMC ADC.
* Sensiron SGP30
  - Modifiers for ethanol and H2.
  - New driver and dt bindings.
  - Follow patch added self cleaning support.
* Sensiron SPS30
  - New channel type for mass concentration.
  - New driver and bindings.
  - Minor tidy up patch followed (drop fmt specifier as unused)
* st_pressure
  - lps22hh support. ID plus information structures and dt bindings.
* ti-ads124s08
  - Add binding doc and driver.

Staging graduations
* ad7606 driver and bindings.

Staging drops
* ad7152 CDC driver dropped.  This part is near EoL and no one is known
  to be using it.  If anyone surfaces obviously we can bring the driver
  back.  If not, good to drop it to avoid wasting anyone's time cleaning
  it up.

New features
* bme680
  - DT support and bindings doc.
* isl29018
  - Add regulator for VCC.
* mag3110
  - Add regulators for supplies.
* meson-saradc
  - Support the temperature sensors of more SoCs.
* mma8452
  - Add regulators for power suplies and binding docs to reflect them.
* st-accel
  - Support the undocumented but it seems fairly common _ONT ACPI method
    to specify orientation of the sensor.

Cleanup, minor fixes and fixes for staging driver that have been broken a
long time
* ad5933
  - Drop platform data alternative to specifying the reference voltage
    using a regulator.
  - Use the clock framework to contorl the reference clock.
  - Add a DT binding doc to cover the defacto binding.
* ad7280a
  - Split up some big functions to improve readability.
* ad7606
  - Allow for timeout if interrupt never occurs.
  - Use devm functions to simplify probe and remove.
  - Use the find_closest macro to avoid need for precise values from
    userspace.
  - Add missing vendor prefixes for various DT properties. Note the
    driver is in staging still and there are no known devicetrees.
  - Add explict OF device ID table.
  - Simplify the Kconfig choices
  - Change to a threaded IRQ.
  - SPDX and simple stype fixes.
* ad7816
  - Drop unnecessary variable init.
* ad9523
  - Check a return value that was ignored.
* ad9833
  - Drop platform data.  It was just setting most values to the hardware
    defaults.
  - Use the clock framework to provide the input clock.
* adt7316 (lots of staging cleanup)
  - Fix some wrong register / bit definitions
  - Invert the logic of the check for an ldac pin so it actually makes sense.
  - Read the right register to get internal vref settings
  - Allow adt751x chips to use the internal vref for all DAC channels rather
    than a subset.
  - Remove dac vref bypass control from parts that don't have one.
  - Make the store DAC update mode function consistent with the show one.
  - Fix some spellings and other minor tidy up.
  - Avoid passing irq numbers around by putting all the irq logic in
    one place.
  - Fix an issue with the resolution of DAC control.
  - Fix support of the high resolution DAC mode (for temp proportional output)
    where supported.
  - Fix DAC read and write calculations.
* st_lsm6dsx
  - Drop an unused variable (set but not read)
* xilinx-xadc
  - Check an unhandled return value.
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