powerpc/85xx: Enable USB2 controller node for P1020RDB

Enable USB2 controller node for P1020RDB. USB2 controller is used only
when board boots from SPI or SD as it is muxed with eLBC

Signed-off-by: Ramneek Mehresh <ramneek.mehresh@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>