sys/dev/sound/pcm/ac97.c:

• Added codec id for CMI9761.
• feeder_volume *whitelist* through ac97_fix_volume()

sys/dev/sound/pcm/ac97.h:

• Added AC97_F_SOFTVOL definition.

sys/dev/sound/pcm/channel.c:

• Slight changes for chn_setvolume() to conform with OSS.
• FEEDER_VOLUME is now part of feeder building process.

sys/dev/sound/pcm/mixer.c:

• General spl* cleanup. It doesn't serve any purpose anymore.
• Main hook for feeder_volume.

Submitted by: Ariff Abdullah <skywizard@MyBSD.org.my>
Tested by: multimedia@