msm: kgsl: Max the expired timestamp of invalidated context

Set the timestamp of an expired context to the maximum which is the
last timestamp that was assigned to a command batch of that context.
This is done so that any events which are registered by the context
will be triggered normally and avoid any sync timeouts.

Change-Id: I0ac4507bcaaa9835dd79ffa8f7066bfff6d3f48d
Signed-off-by: Shubhraprakash Das <sadas@codeaurora.org>