[ALSA] Add snd-portman2x4 driver for Midiman Portman 2x4 MIDI device

snd-portman2x4 driver supports Midiman Portman 2x4 parallel port
MIDI device.

Signed-off-by: Matthias Koenig <mkoenig@suse.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>