usb: gadget: net2280: add USB2380 support

The PLX USB2380 is a PCIe version of the NET2280 and behaves more like the
USB338x but without the USB3.0 superspeed support.

This was tested with g_ether, g_serial, g_mass_storage on a Gateworks
Ventana GW2383.

Cc: Justin DeFields <justindefields@gmail.com>
Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>