msm: mdss: add init and deinit calls to notify update ioctl

Adding notify update init and notify update deinit calls which
ought to be called when the notify update thread is being
started and exited in userspace. The need for these is to ensure
that during exit sequence of the notify update thread there is
minimal wait due to ioctl being blocked in driver. The wait
completions will not be reset if deinit has been called and will
need an init call for them to start working. So when we are
exiting the notify update thread, any block that might happen
due to either a concurrent or a later notify update call is now
handled properly so that the block is either returned early or
is not allowed respectively.

Change-Id: I8212bf058285f5929ebc85d41d6bb12b50e388d9
Signed-off-by: Krishna Chaitanya Parimi <cparimi@codeaurora.org>