Add workaround for conflicting IEC958 controls for HD-audio

Add workaround for conflicting IEC958 controls for HD-audio

When both an SPDIF and an HDMI output are present on HD-audio, both
try to access IEC958 controls with index=0 although one of them must
be wrong.  For avoiding this conflict, the recent kernel code (3.9 and
3.8 stable) moves the IEC958 controls of an SPDIF with index=16 once
when the conflict happens.

In this patch, the corresponding support is added in alsa-lib side.
The new "skip_rest" boolean flag is added to the hooked element
definition which indicates that the rest of element array will be
ignored once when this element is present and evaluated.  With this
new flag, the HD-audio config takes index=16 primarily, then take
index=0 as fallback.

Signed-off-by: Takashi Iwai <tiwai@suse.de>