omap3: beaglexm: fix DVI reset GPIO

GPIO reset line for Beagle XM is different from vanilla beagle
so we populate it as part of gpio update routine.

This in part fixes the issue of display not functioning on beagle XM
platform.

[nm@ti.com: split up, added descriptive changelogs]
Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Koen Kooi <koen@beagleboard.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>