When the HD-audio is removed, it leaves the refcounts when codecs are
powered up (usually yes) in the destructor.  For fixing the unbalance,
and cleaning up the code mess, this patch changes the following:
- change pm_notify callback to take the explicit power on/off state,
- check of D3 stop-clock and keep_link_on flags is moved to the caller
  side,
- call pm_notify callback in snd_hda_codec_new() and snd_hda_codec_free()
  so that the refcounts are proprely updated.

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