arm/dt: pm8941: Add additional VADC channel nodes

Add additional main-mux voltage channel nodes.
The new channels are to support reading the
PMIC die temperature, dc_in, spare channels for
reading the usb_in channel, batt_therm, batt_id
and xo_therm with no pullups.

Change-Id: I8ef2b9fb8b47744eab2c2fd389711011d3a6af58
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>