drm/msm/sde: fix restore handling for encoders

When physical cmd mode encoders are restored after power collapse
the interface flush bits get cleared when the incoming commit
is triggered. This change fixes the trigger kickoff pending
functionality by checking if a restore is in progress. Hw prepare
is handled during the restore phase.

Change-Id: I45253c604edf303eb6fbc3e7fb1110e50b67f1f8
Signed-off-by: Abhijit Kulkarni <kabhijit@codeaurora.org>
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>