[ALSA] Gallant SC-6000 driver

This is port of the Gallant SC-6000 driver from the OSS aedsp16 driver.
This card was also sold as AudioExcel DSP 16 and Zoltrix AV302 (Audio
Plus True 16).

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