hwmon: epm_adc: Remove redundant support

Remove support for ADS ADC that is not used since
the EPM uses the PSoC for getting power measurements.
Update the generic command to use 64 bytes intead of
65 bytes. The generic command is used by the userspace
client to send commands to communicate with the PSoC
and returns the collected buffered samples for requested
power measurements.

Change-Id: I0f2eddd7421888adfeb1c7152e82c96128b7f299
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>