msm: kgsl: Turn cmdbatch->synclist into an RCU list

cmdbatch->synclist is read often for debug purposes so we can easily
turn it into an RCU list and get rid of a lot of the locking. As a
bonus this fixes a warning that was occurring because the the sync
retire function was being called from the dma-fence subsystem with
interrupts turned off.

Change-Id: Ic0dedbad25e9539279e693b1587801935f30a66e
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>