iio: adc: Add QCOM SPMI PMIC5 GEN3 ADC driver

Add support for QCOM SPMI PMIC5 GEN3 ADC driver that supports
hardware based offset and gain compensation.
The ADC peripheral can measure both voltage and current
channels whose input signal is connected to the PMIC ADC AMUX.

The PMIC5 GEN3 ADC peripheral uses registers defined in SDAM.
The register set and configuration have been refreshed compared
to the prior QCOM PMIC7 ADC family.

Change-Id: I3512c3c067d9102406aa92c389d66283f0b12103
Signed-off-by: Jishnu Prakash <jprakash@codeaurora.org>