hwmon: epm_adc: Add EPM support using PSOC

Add support for communicating with the PSOC
using the supported protocol commands from
the PSOC.

The support includes communicating with the
controller to initiate and start the ADC
conversion for the selected channels. Start
and receive ADC conversion for single measurement,
buffered reads, averaging the samples and returning
the results over the set averaging period.

Other commands supported include setting/receiving
the timestamp, setting reference voltage, toggling
gpio to set triggers on set events.

Change-Id: I67ae4ab4378092b8f8de2b1a9d225df89fd0714f
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>