There are probably no reasons left to use Xinerama over xrandr. This
removes the screen based dualhead code and the BIOS Display option in
xorg.conf. Additionally, R128ValidMode() is wrapped so that it can be
aware of multiple displays.
Even though some Crtc functions refer to them, PanelXRes and PanelYRes
should be properties of the Output. If this change to the code seems
awkward, see http://marc.info/?t=107222330700001 for more information.
Signed-off-by: Connor Behan <email@example.com>
Reviewed-by: Alex Deucher <firstname.lastname@example.org>