ALSA: hda - Fix phantom jacks on VT1708

The VT1708 has no unsol event capability, and polling is set using
the "Jack Detect" alsamixer control. In order not to create
phantom Jack controls, temporary enable jackpoll during build_controls.

Signed-off-by: David Henningsson <david.henningsson@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>