msm: mdss: sysfs node to disable smart blit

Add "smart_blit" node in sysfs to enable or disable blit
optimization through adb shell.
"echo 0 > smart_blit" disable smart blit
"echo 1 > smart_blit" enable smart blit

Change-Id: Iae8b46f3ac656ca8f38dbf9f01992e77caf7452d
Signed-off-by: Ramakant Singh <ramaka@codeaurora.org>