arm/dt: pm8019: Add VADC channel nodes

Add new voltage ADC channel nodes to read the ADC from the
USR peripheral of the VADC. The new channel nodes include
reading the pmic die temperature, reference channels for
calibration, XO thermistor, PA thermistors.

Change-Id: I6b406356960e97ee4ffb92a187ffb8beda764dfb
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>