msm: mdp3: move mdp_overlay variable from stack to heap

We are moving struct mdp_overlay variable from stack to heap since
mdp_overlay size increase significantly recently. There
was a warning from compiler saying that frame size is larger than
1024 bytes, which is resolved with this patch. Similar change is
present in mdss code.

Change-Id: Ib19fb63596f095a5a6b2be9b10b5eeb04542449f
Signed-off-by: Terence Hampson <thampson@codeaurora.org>