arm/dt: msm8974: Add vdd_apps for msm_thermal

Add vdd_apps as child node in the device tree.
Once the child node is defined, msm thermal will do voltage
restriction on this rail.

CRs-Fixed: 462816
Change-Id: I405903a588deb3620a56673566e9702f865e89a4
Signed-off-by: Jennifer Liu <chihning@codeaurora.org>