Add QCOM PMIC5 ADC driver

This patch series adds the PMIC5 ADC family of chipset that supports clients to measure voltage on
inputs connected to the PMIC ADC AMUX. Clients include reading voltage phone power and on board system thermistors for thermal management.

The v3 patchset addresses most of the review comments from prior patchset.

Changes since patchset v2
* Removed support for current channel as part of this series.
* Fix pointer arithmetic for iio_chan.
* Few minor changes.
* Update license to SPDX format for ADC header file.

Changes since patchset v1
* Merged DT bindings with prior PMIC family instead of a seperate DT file for PMIC5 family.
* Updated documentation for 'label' and 'value' property.
* Updated using unique prefix adc5 for functions and defines specific for this family of chipset.
* Refactored scaling functions to use function pointer for scaling lookup.
* Added documentation comments as requested in the scaling functions as applicable.
* Added utility functions in the scaling API to avoid some of the code repetitions.
* Use consistent hex format for adc_data and use specific length while assigning data.
* Added support to determine controller version and check against supported hardware settling delay values.
* Various minor changes.

Siddartha Mohanadoss (3):
dt-bindings: iio: adc: Add DT binding document for PMIC5 ADC
iio: adc: Add QCOM SPMI PMIC5 ADC driver
iio: adc: Update QCOM ADC license to SPDX format

 .../devicetree/bindings/iio/adc/qcom,spmi-vadc.txt |  77 +-
 drivers/iio/adc/Kconfig                            |  20 +
 drivers/iio/adc/Makefile                           |   1 +
 drivers/iio/adc/qcom-spmi-adc5.c                   | 864 +++++++++++++++++++++
 drivers/iio/adc/qcom-vadc-common.c                 | 189 ++++-
 drivers/iio/adc/qcom-vadc-common.h                 |  54 ++
 include/dt-bindings/iio/qcom,spmi-vadc.h           | 125 ++-
 7 files changed, 1296 insertions(+), 34 deletions(-)
 create mode 100644 drivers/iio/adc/qcom-spmi-adc5.c

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