ARM: dts: i.MX51: Move usbphy0 node from AIPS1

usbphy0 is not a part of AIPS1, so move this node under root.
Additionally this patch removes useless "status" property.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>