arm/dt: Add VADC_TM channel nodes

VADC_TM is used for monitoring multiple channels with
recurring measurements. Clients can set low/high voltage or
temperature thresholds and receive notification once the
thresholds are crossed. VADC_TM can currently monitor
upto 5 channels. The channel nodes being assigned are for
usb_id, batt_therm, pa_therm's and emmc_therm. Along with
the channel assignments, channel properties for the selected
channels include configuring the sampling rate, pre-div
channel scaling, the scaling function specific to the channel,
hw-settling time.

Change-Id: Iff8167dc347351d03b683196c22f104e0ca29589
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>