msm: kgsl: Track the submitted timestamp for a draw context

Track the last timestamp that each draw context has submitted to
the ringbuffer.  This complete the picture for the draw context
dump:

kgsl-3d0: context[13]: queue=165, submit=115, start=101, retire=100

here, timestamp 165-116 are on the queue, 115-102 are on the
ringbuffer, 101 is in the GPU and 100 and older have been retired.
If we get a fence timeout with this data we can easily see where the
fence timestamp is in the pipeline.

Change-Id: Ic0dedbadf54c1714296149af02b6938eef375d50
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>