defconfig: msm8974: Enable VADC_TM

VADC_TM is used for monitoring multiple channels with
recurring measurements. Clients can set low/high voltage or
temperature threshold and receive notification once the
thresholds are crossed. VADC_TM can currently monitor
upto 5 channels.

Change-Id: I0f6ff3856496966b2933094cff24315dfee8630e
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>