arm: gpiomux-8974: Add epm config

Add gpio configuration for EPM device. EPM is used
for current/voltage measurement for supported channels.
EPM driver provides interface to enable/disable the
device. Existing users enable the device only when
the current/voltage measurement is required.

Change-Id: I79e165405d1e9e996fcd0d4f82302a68221f9f08
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>