Temporary code to enable xhci on acer c720.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
usb: Move default pipe max packet size code from xhci to main code.

Also, the max packet size for super speed devices is 512 bytes (not
256 bytes).

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
xhci: Use the same endpoint initialization code in xhci_alloc_pipe()

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
xhci: Add copyright notice to usb-xhci.c

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>