ARM: dts: Add VADC nodes for SDM855

Clients can request VADC reads for charger related ADC inputs
such as SBUx for watermark detection, MID_CHG, USB_IN_I, USB_IN_V,
PMIC die temperature, charger temperature, smb thermistor, connector
thermistor. Clients can also read VPH_PWR and thermistors connected
to ADC inputs for thermal management. Add VADC channels for PM855B,
PM855 and PM855l.

Change-Id: If27a65250e86c4c1c55401c17a80843406d588de
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>