msm: kgsl: Remove unused common registers

Remove unused common registers. This avoids defining them for
future targets and saves some memory.

Change-Id: I4ba8de623368746695702f60047a8e6136f111b9
Signed-off-by: Tarun Karra <tkarra@codeaurora.org>

Conflicts:
	drivers/gpu/msm/adreno_ringbuffer.c