ALSA: hda - Don't create analog mixer for IDT92HD71bxx

The analog mixer unit on IDT 92HD71Bxx codecs is almost useless
since we use only the direct connections from DAC to pin.

Remove the controls to avoid unneeded confusion as default now.
This can be still back via "analog_mixer = 1" hint.

Signed-off-by: Takashi Iwai <tiwai@suse.de>