MIPS: BCM63XX: Add register definitions for USBD dependencies

The USB 2.0 device depends on some functionality in other blocks, such
as GPIO and USBH.  Add those register definitions here.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Patchwork: http://patchwork.linux-mips.org/patch/4025/
Signed-off-by: John Crispin <blogic@openwrt.org>