msm: kgsl: Dump 64KB of preemption record in snapshot

Dumping only the ctxt_record structure in a snapshot
is not enough. For a more meaningful snapshot, dump 64KB
of preempt record. Also, move the code to device specific
snapshot function.

Change-Id: I43e08ccefbf2d3911191b2aad5168979956e1626
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>