msm: mdss: validate current switch state before commit

If mode switch is currently in progress, then proper state machine of
calls is expected. If these calls are not observed then it could lead
to issues during display commit, because of incomplete update.
Add checks for current mode switch state to prevent improper state
during commit.

Change-Id: I31dae6e15761fc745efd79edbe1070af992db904
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>