ALSA: hda - not choose assigned converters for unused pins of Valleyview

For Valleyview display codec, if an unused pin chooses an assgined converter
selected by a used pin, playback on the unused pin can also give sound to the
output device of the used pin. It's because data flows from the same convertor
to the display port of the used pin. This issue is same as Haswell.

So this patch avoids using assinged convertors for unused pins.
The related function haswell_config_cvts() is renamed for code reuse.

Signed-off-by: Mengdong Lin <mengdong.lin@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>