msm: kgsl: Move events to context specific lists

Move the event accounting from a master list on the device to individual
context lists. This makes the management code more simple and reduces
the amount of extra cycles taken trying to walk a single largish list.
The new added code makes the event code slightly bigger than kgsl.c can
bear. As events become more commonplace this code will be more important
and it will be easier to maintain in a dedicated file so move all the event
related code into kgsl_events.c

Change-Id: Ic0dedbadf00b96eee53aea1d26acb195f1a916ce
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>