ALSA: hda/realtek: Enable audio jacks of ASUS UX391UA with ALC294

By default, there is no sound on Asus UX391UA on Linux.

This patch adds sound support on Asus UX391UA. Tested working by three
different users.

The problem has also been described at
https://bugs.launchpad.net/ubuntu/+source/alsa-driver/+bug/1784485



Signed-off-by: Wandrille RONCE <w@ndrille.fr>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>