drm/msm/sde: Add debugfs support for fence info dump

Add changes to SDE driver to dump fence related information
via debugfs node.

Command to dump the information:
	cat /d/dri/0/crtc*/fence_status

This provides CRTC ID: with fence status, associated connector
fence, and all staged plane fence status.

Change-Id: I3528bb5d864eb045c0c8611cc40e50739f602523
Signed-off-by: Jayant Shekhar <jshekhar@codeaurora.org>