msm: kgsl: Unbind the kgsl-event workqueue

Allow the kgsl-event workqueue to run on any available
core. The other workqueues in KGSL were already unbound.

CRs-Fixed: 985082
Change-Id: I7e843b57541b7ddcb53848078f73b05c88238711
Signed-off-by: Jonathan Wicks <jwicks@codeaurora.org>