[dwusb] Add driver for DesignWare USB3 host controller

[dwusb] Add driver for DesignWare USB3 host controller

Add a basic driver for the DesignWare USB3 host controller as found in
the Lichee Pi 4A.

This driver covers only the DesignWare host controller hardware.  On
the Lichee Pi 4A, this is sufficient to get the single USB root hub
port (exposed internally via the SODIMM connector) up and running.

The driver does not yet handle the various GPIOs that control power
and signal routing for the Lichee Pi 4A's onboard VL817 USB hub and
the four physical USB-A ports.  This therefore leaves the USB hub and
the USB-A ports unpowered, and the USB2 root hub port routed to the
physical USB-C port.  Devices plugged in to the USB-A ports will not
be powered up, and a device plugged in to the USB-C port will
enumerate as a USB2 device.

Signed-off-by: Michael Brown <mcb30@ipxe.org>