hwmon: qpnp-adc: Support configurable pull-ups

VADC peripheral has internal support to select
configurable pull-ups through a configurable AMUX
100k and 150k pull-up. Clients who need the
configurable pull-up include PA_THERM's, XO_THERM's,
EMMC_THERM, MSM_THERM can select the appropriate
channel id to select the 100k/150k pull-up.

Change-Id: I8075b163fe23f0ee942929f0d7f712f3972b9619
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>