ALSA: hda - Support led audio trigger

Now all relevant platform drivers are providing the LED audio trigger,
we can switch the mute LED control with the LED trigger, finally.

For the mic-mute LED trigger, a common fixup function,
snd_hda_gen_fixup_micmute_led(), is provided to be called for the
corresponding quirk entries.  This sets up the capture sync hook with
ledtrig_audio_set() call appropriately.

For the mute LED trigger, which is done currently only for
thinkpad_acpi, the call is replaced with ledtrig_audio_set() as well.

Overall, the beauty of the new implementation is that the whole ugly
bindings with request_symbol() are dropped, and also that it provides
more flexibility to users.

One potential behavior change by this patch is that the mute LED enum
may be created on machines that actually have no LED device.  In the
former code, we did test-call and abort binding if the test failed.
But with the LED-trigger binding, this test isn't possible, and the
actual check is done in the LED class device side.  So it's the
downside of simpleness.

Also, note that the HD-audio codec driver doesn't select CONFIG_LEDS
and co by itself.  It's supposed to be selected by the platform
drivers instead.

Acked-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Acked-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>