Add new support for ALC257 codec.

[ It's supposed to be almost equivalent with other ALC25x variants,
  just adding another type and id -- tiwai ]
Signed-off-by: Kailang Yang <kailang@realtek.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>