Add support for YWRAP scrolling by shuffling pages around in DMM
instead of sw blits.

Note that fbcon only utilizes this mode if the y resolution is
divided evenly by the font height.  So, for example, a 1920x1080
display using a 16 pixel tall font will not utilize this, but a
1280x1024 display would.
Signed-off-by: Rob Clark <rob@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>