beagleboard: enable HUB power on all variants of the BeagleBoard

beagleboard: enable HUB power on all variants of the BeagleBoard

Changes made by Jason Kridner with inputs from Eric Benard to special case xM Rev A and xM Rev B

Relevant discussions:
http://www.mail-archive.com/u-boot@lists.denx.de/msg59361.html
http://www.mail-archive.com/u-boot@lists.denx.de/msg59589.html

Signed-off-by: Joel A Fernandes <joelagnel@ti.com>
Cc: Eric Benard <eric@eukrea.com>
Cc: Christian Spielberger <c.spielberger@bct-electronic.com>
Cc: Jason Kridner <jdk@ti.com>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>