msm: kgsl: Do not allow events with bogus timestamp

Do not register an event if the timestamp of that event is greater
than the highest timestamp assigned to the context or global in
case of global event

Change-Id: If12ad2dbc579bbcf7e99b3179ab8f911dc9b41aa
Signed-off-by: Shubhraprakash Das <sadas@codeaurora.org>