msm: mdss: Don't allow any ioctls during dynamic switch

Don't allow any ioctls like DISPLAY_COMMIT, OVERLAY_SET,
OVERLAY_PLAY when dsi dynamic switch is underway, to avoid
any stability issues.

Change-Id: I66e68e399c1fb31e7b9dcd3a4840d4fe59a58914
Signed-off-by: Sandeep Panda <spanda@codeaurora.org>