powerpc/83xx: Add USB Host support for MPC8360E-RDK boards

Simply add the usb node to support USB host on the MPC8360E-RDK
boards.

Currently U-Boot doesn't fill the clock-frequency property for
timer nodes, so for now we have to fill it manually.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>