usb: gadget: bcm63xx UDC driver

Driver for the "USB20D" / "USBD" block on BCM6328, BCM6368, BCM6816,
BCM6362, BCM3383, and others.

The hardware block was designed to support networking applications
(direct connection of a home router to a PC), and the endpoint
configuration is fixed.

[ balbi@ti.com : dropped USB_GADGET_DUALSPEED from Kconfig ]

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Acked-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Signed-off-by: Felipe Balbi <balbi@ti.com>