ALSA: hda/realtek - Simplify the output volume initialization

Simplify the output path initialization using the existing path
information instead of assuming the topology specific to Realtek
codecs.  This is also implicitly a fix for some amp values on output
pins where the old parser missed (e.g. ALC260 output pins).

The same function alc_auto_set_output_and_unmute() can be used now for
the multi-io activation, since the output selection means nothing but
activating the given output path.

And, finally at this stage, we can get rid of alc_go_down_to_selector()
and other functions that are codec really specifically to Realtek
codecs.

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