ARM: dts: msm: Add VADC channels for PMI632

Clients of VADC_HC include reading voltage phone power, system
thermistors for thermal mitigation. Add VADC node and supported
channels for PMI632.

Change-Id: I75a7ffbef5e2751c4b5b94e972b14ff43400d6e8
Signed-off-by: Jishnu Prakash <jprakash@codeaurora.org>