The dual-headphone mode with STAC/IDT codecs is useful only for machines
that have two (or more) built-in headphones.

But, some HP laptops give multiple headphone pin configs, one for the
built-in and another for the separate (likely a docking station) one.
This results in a missing speaker volume control.

This patch adds more check for the dual-headphone mode to avoid this
problem.

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