ALSA: hda - Share digital I/O parser in patch_realtek.c

Make a helper function to parse the digital I/Os of all Realtek codecs
to simplify the code and to ensure the setups.
Also, initialize digital I/O pins properly in init callbacks.  Some BIOS
seem to leave pins uninitialized.

Signed-off-by: Takashi Iwai <tiwai@suse.de>