msm: kgsl: add debugfs context files

Add a file for every context under /d/kgsl/kgsl-3d0/ctx/<id>.
This file prints timestamps, cmdbatches, fences and events
that are pending, to aid with debugging of fence issues.
Repeatedly reading this file will likely reduce performance
due to the many locks that must be held.

Change-Id: I70c7a5f2d3cc1251587a1f2172b956b11286bd92
Signed-off-by: Jeremy Gebben <jgebben@codeaurora.org>