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>