msm: kgsl: Add multiple ringbuffers

Detach the adreno driver from the concept of a single static
ringbuffer and allow the use of multiple ringbuffers. For
now only the first ringbuffer is used. This is in
anticipation of hardware preemption feature which will use
the additional ringbuffers based on context priority.

Change-Id: I0a9e329851c7dc7fce681552fb4101ab80be6cb1
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Shubhraprakash Das <sadas@codeaurora.org>