msm/sde: Unregister input handler during encoder disable

Flush and unregister input handler in encoder disable and register
again in encoder enable. This is done to ensure that input
handler doesn't work during suspend mode.

Change-Id: I457a7e88bdf3bfd966da69edc81d14584dbeb784
Signed-off-by: Shubhashree Dhar <dhar@codeaurora.org>