msm: kgsl: Add ability to wait for ringbuffer timestamp

Add functionality to wait for a ringbuffer timestamp to
expire. Also, unify the rb events into a single event
group instead of maintaining 2 seperate groups.

Change-Id: I7c6742147e072a99008bf1b5cab0884adc4da308
Signed-off-by: Shubhraprakash Das <sadas@codeaurora.org>