Set up channel information for HDMI widgets.  This will allow LPCM
with multiple channels supported on some HDMI devices.

TODO: It still doesn't check ELD and doesn't change PCM parameters
dynamically.
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>