ALSA: hda/realtek - Improved routing for Thinkpad X1 7th/8th Gen

There've been quite a few regression reports about the lowered volume
(reduced to ca 65% from the previous level) on Lenovo Thinkpad X1
after the commit d2cd795c ("ALSA: hda - fixup for the bass speaker
on Lenovo Carbon X1 7th gen").  Although the commit itself does the
right thing from HD-audio POV in order to have a volume control for
bass speakers, it seems that the machine has some secret recipe under
the hood.

Through experiments, Benjamin Poirier found out that the following
routing gives the best result:
* DAC1 (NID 0x02) -> Speaker pin (NID 0x14)
* DAC2 (NID 0x03) -> Shared by both Bass Speaker pin (NID 0x17) &
                     Headphone pin (0x21)
* DAC3 (NID 0x06) -> Unused

DAC1 seems to have some equalizer internally applied, and you'd get
again the output in a bad quality if you connect this to the
headphone pin.  Hence the headphone is connected to DAC2, which is now
shared with the bass speaker pin.  DAC3 has no volume amp, hence it's
not connected at all.

For achieving the routing above, this patch introduced a couple of
workarounds:

* The connection list of bass speaker pin (NID 0x17) is reduced not to
  include DAC3 (NID 0x06)
* Pass preferred_pairs array to specify the fixed connection

Here, both workarounds are needed because the generic parser prefers
the individual DAC assignment over others.

When the routing above is applied, the generic parser creates the two
volume controls "Front" and "Bass Speaker".  Since we have only two
DACs for three output pins, those are not fully controlling each
output individually, and it would confuse PulseAudio.  For avoiding
the pitfall, in this patch, we rename those volume controls to some
unique ones ("DAC1" and "DAC2").  Then PulseAudio ignore them and
concentrate only on the still good-working "Master" volume control.
If a user still wants to control each DAC volume, they can still
change manually via "DAC1" and "DAC2" volume controls.

Fixes: d2cd795c

 ("ALSA: hda - fixup for the bass speaker on Lenovo Carbon X1 7th gen")
Reported-by: Benjamin Poirier <benjamin.poirier@gmail.com>
Reviewed-by: Jaroslav Kysela <perex@perex.cz>
Tested-by: Benjamin Poirier <benjamin.poirier@gmail.com>
Cc: <stable@vger.kernel.org>
BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=207407#c10
BugLink: https://gist.github.com/hamidzr/dd81e429dc86f4327ded7a2030e7d7d9#gistcomment-3214171
BugLink: https://gist.github.com/hamidzr/dd81e429dc86f4327ded7a2030e7d7d9#gistcomment-3276276
Link: https://lore/kernel.org/r/20200829112746.3118-1-benjamin.poirier@gmail.com
Link: https://lore.kernel.org/r/20200903083300.6333-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>