usb: move r8a66597 register defines

Move r8a66597 hardware register definitions from the host
controller header file to the platform data header file.

With this change in place we can easily share register
definitions between the host controller driver and a future
gadget driver.
Signed-off-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>