msm: kgsl: let postmortem dump find context switch IBs

Because the IBs used for context switching are not allocated
by userspace, a separate search is needed to find them
in adreno_find_region.

Change-Id: I4c2a180333ae54ecbf257fd8c90ec2e3f748ad95
Signed-off-by: Jeremy Gebben <jgebben@codeaurora.org>