drm/msm: move dynamic fps and seamless updates

Move DSI/INTF updates for dynamic FPS and seamless operations
from 'mode_set' to the pre-enable/enable part of the commit
sequence.

This is done so that we can split the atomic commit sequence into
'prepare' and 'commit' stages separated by the CRTC's atomic_flush
callback.

Also remove previously added support for 8996-specific 'quirks'.

Change-Id: I7ba3e48a1cf22d4f329844153eca89e76674e96b
Signed-off-by: Clarence Ip <cip@codeaurora.org>