ALSA : hda - not use assigned converters for all unused pins

BIOS can mark a pin as "no physical connection" if the port is used by an
integrated display which is not audio capable. And audio driver will overlook
such pins.

On Haswell, such a disconneted pin will keep muted and connected to the 1st
converter by default. But if the 1st convertor is assigned to a connected pin
for audio streaming. The muted disconnected pin can make the connected pin
no sound output.

So this patch avoids using assigned converters for all unused pins for Haswell,
including the disconected pins.

Signed-off-by: Mengdong Lin <mengdong.lin@intel.com>
Reviewed-by: David Henningsson <david.henningsson@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>