Merge branch 'topic/hda-micmute-led' into for-next

This is a patch set inspired by the recent patch Kai-Heng posted about
the HD-audio mic-mute LED control.  Currently HD-audio driver deals
with the mute and mic-mute LED in several different ways: primarily
with the direct callback of vmaster hook and capture sync hook, while
another with the LED class device binding.  The latter has been used
for binding with the platform device LEDs like Thinkpad, Dell,
Huawei.  And, yet, recently we added our own LED classdev for the
mic-mute LED on some HP systems although they are controlled directly
with the callback; it's exposed, however, for the DMIC that is
governed by a different ASoC driver.

This patch set is an attempt to sort out and make them consistent:
namely,
* All LEDs are now controlled via LED class device
* The generic driver provides helper functions to easily build up the
  LED class dev and the relevant mixer controls
* Conversion of the existing framework and clean ups

The patches are lightly tested in my side with a couple of machines
and also through hda-emu tests.  Some devices receive new kcontrols
for the mute LED behavior (that have been missing so far), but
anything else look good though my tests.

Link: https://lore.kernel.org/r/20200618110842.27238-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>