msm: kgsl: Allow sync points to be created on the submitter's context

There are situations where a submitting thread may wish to create a
syncpoint on an already issued timestamp to pause a context until a
previous command has been retired.  Relax the restriction against
submitting a sync point against one's own context and only check to
make sure the user isn't submitting a syncpoint against a future
timestamp (which would be a certain deadlock).

Change-Id: Ic0dedbad883fc228da0d94c8416a88504f5d1377
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>