When a headphone jack is configurable as input, the generic parser
tries to make it retaskable as Headphone Mic.  The switching can be
done smoothly if Capture Source control exists (i.e. there is another
input source).  Or when user explicitly enables the creation of jack
mode controls, "Headhpone Mic Jack Mode" will be created accordingly.

However, if the headphone mic is the only input source, we have to
create "Headphone Mic Jack Mode" control because there is no capture
source selection.  Otherwise, the generic parser assumes that the
input is constantly enabled, thus the headphone is permanently set
as input.  This situation happens on the old MacBook Airs where no
input is supported properly, for example.

This patch fixes the problem: now "Headphone Mic Jack Mode" is created
when such an input selection isn't possible.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=65681
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>