ALSA: opti-miro: add PnP detection

The PCM12 and PCM20 can be set into the ISA PnP mode. The PCM12 PnP
was sold as the PnP device.
Add code to handle detection of these cards using ISA PnP framework.

Tested on the PCM20 in PnP mode. The PCM12 PnP has the same MS Windows
INF file except for a card name displayed for user.

Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: Takashi Iwai <tiwai@suse.de>