drm/msm/sde: remove frame_done_timer logic from encoder

The frame_done_timer logic is redundant to detect the frame
completion failures, as there are already wait_fn for the
required IRQs for all panel modes(video/cmd/wb).

Change-Id: I06f2a1efc329771351b5c28b6ad64a2246336bce
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>