ALSA: hda - Drop bind-volume workaround

The bind-volume workaround was introduced for simplifying the mixer
abstraction in the case where one or more pins of multiple outputs
lack of individual volume controls.  This was essentially the case
like Acer Aspire 5935, which has 5.1 speakers and 5.1 (multi-io)
jacks although there are 5 DACs, so some of them must share a DAC.

However, the recent code rewrite changed the DAC assignment policy to
share with the same channel instead of binding to the front, thus
binding the volumes for all channels makes little sense now, rather
it's confusing.  So in this patch, the ugly workaround is finally
dropped and simply create the volume control corresponding to the
parsed path position.

For dual headphones or 2.1 speakers with a shared volume control, it's
anyway bound to the same DAC if needed, so this change shouldn't bring
any practical difference.

And, as a good bonus, we can cut off the whole code handling the bind
volume elements.

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