msm: kgsl: Add support for device tree in kgsl

Populate the platform_data structure by reading from the Device Tree
Source file.

Change-Id: Ic8c83d3918510448b76559b095ad414d2f22c7bd
Signed-off-by: Lokesh Batra <lbatra@codeaurora.org>
msm: kgsl: Change vdd_dig to vddcx

Change GPU digital circuit head switch name to vddcx to match
devicetree property name convention.

Change-Id: If17b47125f08873106f74fdb21a29c58dbf1496a
Signed-off-by: Pu Chen <puchen@codeaurora.org>