HID: Add driver for Retrode2 joypad adapter

This driver does 2 things:

 - Apply the MULTI_INPUT quirk to create separate joypad device nodes
   for each one of the 4 connectors.
 - Rename the input devices so that their names are different, and allow
   users to recognise which device corresponds to which physical port,
   including the SNES (Mario Paint) Mouse.

Signed-off-by: Bastien Nocera <hadess@hadess.net>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>