hwmon: pm8xxx-adc: Add PM8018 ADC Driver

PM8921 and PM8018 have a common ADC module. Difference's
are in the channel supported on individual PMIC's and
in the MPP mapping to the ADC device.
MPP configuration on PM8018 is not required. The MPP
is directly connected to the AMUX pre-mux channel.

Change-Id: I9aed3366f20e3985962119274d8b2865b7054a79
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>
5 files changed