ALSA: hda: hdmi - preserve non-MST PCM routing for Intel platforms

Commit 5398e94f

 ("ALSA: hda - Add DP-MST support for NVIDIA codecs")
introduced a slight change of behaviour how non-MST monitors are
assigned to PCMs on Intel platforms.

In the drm_audio_component.h interface, the third parameter
to pin_eld_notify() is pipe number. On Intel platforms, this value
is -1 for MST. On other platforms, a non-zero pipe id is used to
signal MST use.

This difference leads to some subtle differences in hdmi_find_pcm_slot()
with regards to how non-MST monitors are assigned to PCMs.
This patch restores the original behaviour on Intel platforms while
keeping the new allocation policy on other platforms.

Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Link: https://lore.kernel.org/r/20191129143756.23941-2-kai.vehmanen@linux.intel.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>