ALSA: hda/realtek - Support low power consumption for ALC256

Remove hp_pin = 0 return. Add the default pin 0x21 as headphone.
Supported low power consumption, it must do depop procedure when
headset jack was plugged or unplugged.
So, alc256_init() and alc256_shutup() must run delay when headset jack
was plugged or unplugged.
If depop procedure not run with delay, it will have a chance to let
power consumption raise high.

[ NOTE: this is a quite quite similar change for ALC295 by commit
  d3ba58bb ("ALSA: hda/realtek - Support low power consumption for
  ALC295"), but applied to ALC256 codec instead -- tiwai ]

Fixes: 8983eb60

 ("ALSA: hda/realtek - Move to ACT_INIT state")
Signed-off-by: Kailang Yang <kailang@realtek.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>