msm: mdss: wait for idle when wait for kickoff not available

When underlying mdp driver doesn't support waiting for kickoff trigger,
wait for panel to be idle instead. This will ensure proper
synchronization of updates.

Change-Id: I8fcb75c1873cd55b1aade3442aa99c6c1eba62a8
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>