omap3: beaglexm: fix EHCI power up GPIO dir

EHCI enable power pin is inverted (active high) in comparison
to vanilla beagle which is active low. Handle this case conditionally.

Without this fix, Beagle XM 4 port EHCI will not function and no
networking will be available

[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>