Staging: udlfb: add dynamic modeset support

Add dynamic modeset support

udlfb uses EDID to find the monitor’s preferred mode
udlfb no longer has fixed mode tables – it’s able to set any mode
dynamically, from the standard VESA timing characteristics of the monitor.

Draws from probe and setmode code of both displaylink-mod 0.3 branch of
Roberto De Ioris, and Jaya Kumar's displaylinkfb.
Lays foundation for defio support and making backbuffer optional.
With additional changes to minimize diffs and clean for checkpatch.pl style.

Does not yet include new ioctls or refcount/mutex code from displaylink-mod.

Tested to work with existing xf-video-displaylink X server unmodified.

Signed-off-by: Bernie Thompson <bernie@plugable.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>