msm_fb: display: add ioctl for mixer info

Add new ioctl to allow user to query mdp mixer detail configuration.

Change-Id: Id40a943ffa86eb3c97ef6b7bd00f0b01ab35867f
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>
Merge "msm_fb: display: add ioctl for mixer info" into cm-10.1