msm: kgsl: set GPU register RB_GMEM_BASE_ADDR

GPU register RB_GMEM_BASE_ADDR needs to be initialized with GMEM base
address. From A330, OCMEM is utilized to be GMEM dynamically; when
OCMEM is allocated for GFX, the allocated region address may vary
every time, GPU register RB_GMEM_BASE_ADDR need to be initialized
with the allocated OCMEM region address.

Change-Id: I5cb4472a9f18759d2af160a15d83f1404378a530
Signed-off-by: liu zhong <zhongl@codeaurora.org>