ASUS TM420 had depop circuit for headphone.
It need to turn on by COEF bit.

[ fixed the missing enum definition by tiwai ]
Signed-off-by: Kailang Yang <kailang@realtek.com>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/3d6177d7023b4783bf2793861c577ada@realtek.comSigned-off-by: Takashi Iwai <tiwai@suse.de>