Second set of new device support, features and cleanup for IIO in the 4.17 cycle

The uptick in staging cleanup is partly due to GSoC Applications
process being underway and one of Daniel's tasks being to try
cleaning up an IIO driver to move out of staging.
Naturally there is some normal staging cleanup progress in here
as well.

New device support
* Microchip mcp4018
  - New driver supproting MCP4017, MCP4018 and MCP4019 digital pots.
* On Semiconductor lv0104cs
  - New driver to support this ambient light sensor.

Cleanup
* axp20x_adc
  - remove a !! in favour of clear ternary operator.
* ad2s1210 (staging cleanup)
  - Reorganise to avoid ending a line with [
  - Remove some unnecessary defines.
  - Remove unsed variable.
* ad5380
  - Replace magic 0 with IIO_CHAN_INFO_RAW
* ad5764
  - Replace magic 0 with IIO_CHA_INFO_RAW
* ad7150 (staging cleanup)
  - Align arguements with parenthesis.
* ad7152 (staging cleanup)
  - Align arguements.
* ad7746 (staging cleanup)
  - Align arguements.
* ad7816
  - Remove pointless void pointer cast.
* ade7753
  - Replace IIO_DEV_ATTR_CH_OFF with equivalent to avoid confusing
    checkpatch (this macro didn't really help anyway).  Also drop the
    macro from the meter.h header.
* ade7754 (staging cleanup)
  - Add names to funciton definition arguements.
  - Align arguements with open parenthesis where possible.
* ade7758 (staging cleanup)
  - Remove __func__ from dev_dbg statements as provided by dynamic
    debug anyway.
  - Align arguements with open parenthesis where possible.
* ade7759 (staging cleanup)
  - Replace IIO_DEV_ATTR_CH_OFF with equiavalent to avoid confusing
    checkpatch.
* adis16201 (staging cleanup)
  - Headers in alphabetical order.
  - Blank lines before returns.
* adis16209 (staging cleanup)
  - Headers in alphabetical order
  - Change some definition names to make them more meaningful (2 rounds
    of this).
  - Add explicit _REG prefix to register names to make them
    obviously different from fields within those registers.
  - Remove some superflous comments and group definitions better.
  - Use a switch statement to make it semantically obvious that we
    only have two options (rather than an unlimited 'else').
  - Use sign_extent32 instead of open coding.
* adt7316 (staging cleanup)
  - Move an export next to symbol.
* bmc150
  - drop redundant __func__ in dynamic debug.
* ccs811
  - Rename varaible to better reflect what it does.
* cros_ec
  - Reduce sampling frequency before suspending to avoid preventing
    suspend.
* dummy
  - Correct whitespace in Kconfig.
  - Add extra description in Kconfig.
* ds1803
  - Remove a VLA which we always know is 2 long.
* hid-sensor-accel
  - Replace magic number 0 by IIO_CHAN_INFO_RAW.
* hid-sensor-gyro
  - Replace magic number 0 by IIO_CHAN_INFO_RAW.
* hid-sensor-light
  - Replace magic number 0 by IIO_CHAN_INFO_RAW.
* hid-sensor-magn
  - Replace magic number 0 by IIO_CHAN_INFO_RAW.
* lm3533
  - Replace magic number 0 by IIO_CHAN_INFO_RAW
* mlx90632
  - Squash a smatch warning - no runtime effect.
* stm32_dfsdm:
  - Cleanup the dt bindings.
* sx9500
  - Add GPIO ACPI mapping table to behave correctly when firmware
    doesn't provide the mapping.
* tsl2x7x (staging cleanup)
  - Fix the proximity sensor functionality.
  - Remove platform data provided power functions.  There are much
    better ways to do this these days.
  - Introduce some common functions to avoid various repititions.
  - Stop using mutex_trylock when mutex_lock and wait a bit is fine.
  - Improve error handling in various places.
  - Drop some 'Camel case' (which wasn't actually strickly camel case
    but was a bit odd.
  - Drop some _available sysfs attributes for things that don't exist
    (for particular supported parts).
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