branches: 1.1.2; 1.1.4;
wii: Add support for using a USB Gecko as serial console.

The USB Gecko is a Wii/Gamecube development tool which connects to the
GameCube memory slot of the Wii and a USB port of a computer. The USB
port exposes an FTDI serial port on the computer side of the connection.

EXI commands sent from the Wii to the USB Gecko can read and write bytes.
Wire this up to form a simple serial console when the device is detected.
Use WSDISPLAY_MULTICONS to allow for simultaneous use of the USB Gecko
and the framebuffer console.