ack detection

Since jack detection requires the input subsystem which may not be
desired on small systems it is not built unless required by a driver
that is being built. Drivers using jack detection should use a pattern
like this:

config SND_FOO
        tristate "..."
        ...
        select SND_JACK if INPUT=y || INPUT=SND

to ensure that the jack detection API is enabled if the input subsystem
is.  If the input subsystem is not enabled then a stub version of the
API is provided.

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