msm: mdss: implement overlay prepare ioctl

Overlay prepare will allow a full frame with multiple overlays to be
configured at once and perform frame level checks before being pushed to
display. This function guarantees that if the call is successful, the
frame can be displayed successfully on the screen when display commit is
called.

Change-Id: I276b6fe3e0a872a2e93170f3cea1002d3ce0dac9
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>