ALSA: hda/realtek - Small code cleanups

A few clean-ups for post-static-quirk time:
- Call alc_auto_init_std() statically in alc_init() instead of setting
  spec->init_hook in each caller.  spec->init_hook field is left
  unused for any future use.

- Move the call of set_capture_mixer() to to alc_parse_auto_config()
  instead of each caller.

- Get rid of the ADC-filling and imux check in each parser function.
  This is no longer needed since the auto-parser always check ADCs and
  imux.  It was only for the static quirks.

- Kill unused defines

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