msm: kgsl: Make the GPU device aware of the next pending event

The adreno core needs to know what the next event pending for
any given context is so it can mark the interupt to be fired.
If this isn't done then some timestamps that don't have a
matching waittimestamp call won't fire an interrupt. This is
dangerous on the last interrupt/event before a context goes
away.

Change-Id: Ic0dedbad71f6de07b43b0656128c76509326d645
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>