alsa: Jack detection kcontrol implementation

Support the new jack detection interface implemented in Linux 3.3
(and Ubuntu's 3.2 kernel).

Jacks are probed and detected using the snd_hctl_* commands, which
means we need to listen to them using fdlists. As this detection
needs to be active even if there is currently no sink for the jack,
so this polling is done on the card level.

Also add configuration support in paths, like this:
[Jack Headphone]
required-any = any

...where 'Jack Headphone' should match 'Headphone Jack' as given by
ALSA (as seen in e g 'amixer controls').
"Required", "required-any" and "required-absent" is supported. Using
required-any, one can have several ports even though there is no
other indication in the mixer that this path exists.

Signed-off-by: David Henningsson <david.henningsson@canonical.com>

src/modules/alsa/mixer/paths/analog-input-rear-mic.conf

@@ -22,6 +22,9 @@
 priority = 82
 name = analog-input-microphone-rear
 
+[Jack Rear Mic]
+required-any = any
+
 [Element Rear Mic Boost]
 required-any = any
 switch = select