msm: mdss: Add atomic commit support for MDP3 driver

Atomic commit IOCTL adds validate and commit layer support
for framebuffer driver clients. Clients sends the validate
request with layer list for each display to put layers in
validate list. Once layers are validated; clients sends the
commit request for all validated layers. Validate request
may fail while commit must not fail because clients have
no fall back mechanism for commit failure.

If clients calls the atomic commit without validate request
then commit will validate all the layers before kickoff. In
such situation; commit may fail due to validate failure.

Change-Id: If5b6e3afcded909b6a3096edddec85148634274b
Signed-off-by: Jayant Shekhar <jshekhar@codeaurora.org>