disp: msm: sde: avoid input handler registration in video mode

Input handler is used for early wakeup of DSI and MDP clocks from
idle power collapse. DSI clock won't be disabled in video mode
during idle power collapse, so the input hanlder isn't needed
for video mode.
This change avoids the input handler to be registered in
video mode.

Change-Id: Id23bad192b6671126978d707db464e7aaee1c77f
Signed-off-by: Lei Chen <chenlei@codeaurora.org>