ALSA: hda/realtek - Add ALC256 HP depop function

Add this functions, it could support ALC256 for HP depop functions.
It also can solve some ALC256 machine plug headset cause power
off issue.

Signed-off-by: Kailang Yang <kailang@realtek.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>