specific snd_mixer device rather than global across all mixers.
- Add per-mixer mute status and saved mute_level so that the mixer_hwmute()
function can now toggle the mute state when the mute button is pressed.
- Create a dynamic sysctl tree hw.snd.pcmX when a pcm device is registered.
- Move the hw.snd.hwvol_* sysctl's to hw.snd.pcmX.hwvol_* so that they
are now properly device-specific. Eventually when the mixers become
their own devices these sysctl's will move to live under a mixerX tree.
- Change the interface of the hwvol_mixer sysctl so that it reports the
name of the current mixer device instead of the number and is settable
with the name instead of the number.
- Add a new function mixer_hwinit() used to setup the dynamic sysctl's
needed for the hwvol support that can be called by drivers that support
hwvol.
Reviewed by: cg
a7d7562a91