msm: kgsl: Implement fast preemption for 5XX

Allow 5XX targets to preempt quickly from an atomic context. In
particular this allows quicker transition from a high priority
ringbuffer to a lower one without having to wait for the worker
to schedule.

Change-Id: Ic0dedbad01a31a5da2954b097cb6fa937d45ef5c
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>