msm: kgsl: Add the A6XX preemption buffers to snapshot

Dump a block of the preemption buffers of every ringbuffer. This helps
in debugging preemption issues.

Change-Id: Ib56e2fc0ef926853b36d70f54f3403b8feb02994
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>
Signed-off-by: Mohammed Mirza Mandayappurath Manzoor <mmandaya@codeaurora.org>