msm: vidc: (Re-)Centralise event notifications

kernel_event_queue needs to be woken up each time v4l2_queue_event_fh is
called.  Helper function to facilitate this was private within common.c.
This commit makes it available to rest of the driver.

Change-Id: Ide050d06841857e00ea7f7ecacd6a2101c8a4115
Signed-off-by: Deva Ramasubramanian <dramasub@codeaurora.org>