ALSA: hda - Refactor pm notification in hda_codec.c

No functional change.

- codec->pm_down_notified flag is renamed to codec->pm_up_notified
  flag (and takes the reversed meaning), which is managed solely in
  hda_call_pm_notify() now.

- The explicit call of hda_call_pm_notify() is moved into
  hda_keep_power_on().

- Removed a redundant call of hda_call_pm_notify() in
  snd_hda_power_up(), as it's called in hda_call_codec_resume()
  anyway.

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