ALSA: hda - Enable surround speakers (when line out is also present)

In the case where we have both line out and more than stereo speakers,
the speaker DACs will end up in extra_out_nid.
In fact, AFAIU, speakers are the only ones that can end up in extra_out_nid,
and if we have several of those, they should be surround outputs
rather than copy front.

BugLink: https://bugs.launchpad.net/bugs/1236965
Signed-off-by: David Henningsson <david.henningsson@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>