sh: add r8a66597 usb1 gadget to the se7724 board

Add USB gadget support for port CN26 on the Solution Engine 7724
board. The r8a66597-udc driver is hooked up as a platform device
and some registers are configured to enable the USB in gadget mode.
The hardware driving the USB port is the on-chip USB1 block in
the sh7724 processor configured as USB gadget controller.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>