ALSA: ASoC: Allow machine drivers to mark pins as not connected

Add a new API call snd_soc_dapm_nc_pin() which allows machine drivers to
mark pins as being permanently disabled.  At present this is identical
to snd_soc_dapm_disable_pin() except in terms of improving the internal
documentation of machine drivers that use it.  The intention is that in
future it will be extended to provide additional features such as hiding
controls that are only relevant to paths using the disconnected pin.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>