msm: mdss: add overlay prepare compat ioctl

Add compat layer for OVERLAY_PREPARE ioctl
implementation in MDSS driver. This allows
for 32-bit user process to call the prepare
ioctl in a 64-bit kernel.

Change-Id: I4effef4e43184b9eeb9054447d99ba9adb5f3857
Signed-off-by: Jeevan Shriram <jshriram@codeaurora.org>
Signed-off-by: Manoj Rao <manojraj@codeaurora.org>