arm/dt: msm8974: Add VADC node

Add device tree VADC main node and channel properties
for clients to issue ADC read requests.

Change-Id: Ia75836a240af7d2fea0ea6136640d0c8e379accc
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>
1 file changed