ALSA: ALSA driver for SGI HAL2 audio device

This patch adds a new ALSA driver for the audio device found inside
many older SGI workstation (Indy, Indigo2). The hardware uses a SGI
custom chip, which feeds two codec chips, an IEC chip and a synth chip.
Currently only one of the codecs is supported. This driver already has
the same functionality as the HAL2 OSS driver and will replace it.

Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>