msm: kgsl: Allow a draw context to skip snapshot

Some test applications intentionally generate a GPU fault for
various reasons. Because a GPU fault generates a snapshot and
snapshots are persistent until they are pulled, running the test
application may take up the snapshot slot and prevent a real fault
from being captured and debugged.

This flag allows the draw context to intentionally avoid generating
a snapshot.

Change-Id: Ic0dedbad8476c308a13572d999540b243d97eabc
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>