drm/msm/sde: move sde encoder to new display interface

Call panels via common display-manager interface rather than directly.

Change-Id: I4fe86b6b206929217c0cf807a93287140d507e6c
Signed-off-by: Clarence Ip <cip@codeaurora.org>
Signed-off-by: Krishna Srinivas Kundurthi <kskund@codeaurora.org>