[ALSA] hda-codec - Fix handling of multiple capture streams

Fixed the bug that multiple capture streams conflict on Realtek codec
routines.
Also, this adds a framework to enable the alternative playback stream,
e.g. for VoIP.  It's not fully implemented yet, though.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>