ALSA: hda - hdmi create spdif ctl based on pcm

SPDIF ctl should be based on pcm. Each spdif ctl controls
one pcm state.

This patch creates spdif based on pcm and no longer
based on pin.

Signed-off-by: Libin Yang <libin.yang@linux.intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>