msm: kgsl: Add support for voting vdd parent supply voltage

For RPM based targets which have the dedicated GFX rails
requires voting of vdd parent supply. Hence add support
to vote for vdd parent supply.

Change-Id: I3301b9b5f07d8e928a64b7013ec40b7c54e596ca
Signed-off-by: Hareesh Gundu <hareeshg@codeaurora.org>