Add support for Starr Labs USB MIDI devices such as the Z7S, which are
based on an FTDI serial UART chip.

Based on a patch by Daniel Mack.
Signed-off-by: NKristian Amlie <kristian@amlie.name>
Acked-by: NDaniel Mack <zonque@gmail.com>
Signed-off-by: NClemens Ladisch <clemens@ladisch.de>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>