msm: mdss: reset overlay state when display is off

Client might turn off the display directly, without
releasing the overlay resource.  This is to reset
overlay status when display is being turned off.

CRs-Fixed: 492706
Change-Id: I428f6d1e2b53c7c1379ac8820ab23d8573ae7f1d
Signed-off-by: Xiaoming Zhou <zhoux@codeaurora.org>