msm: mdss: move unstaging of overlay surfaces to display commit

Perform cleanup of surfaces destroyed with overlay unset until next
display update. This enables a smooth transition in case multiple
surfaces are unset before next frame update.

CRs-Fixed: 406645
CRs-Fixed: 406553
Change-Id: I843c7f11fc943d8351b7408116101ba20f25d116
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>