ASoC: SOF: Intel: hda: allow operation without i915 gfx

Add support to configure the HDA controller with an external HDA
codec even if iDisp codec in i915 is not available.

This can happen for multiple reasons:
 - internal graphics is disabled on the system
 - i915 driver is not enabled in kernel or it fails to init
 - i915 codec reports error in HDA codec probe
 - HDA codec driver probe fails

Address all these scenarios, but keep using the existing topology.
In case failures occur, HDMI PCM nodes are created, but they will
report error if application tries to use them. No ALSA mixer controls
are created. If the external HDA codec init fails as well, SOF probe
will return error as before.

Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=206085
BugLink: https://bugzilla.opensuse.org/show_bug.cgi?id=1163677
BugLink: https://github.com/thesofproject/linux/issues/1658
Link: https://lore.kernel.org/r/20200220171028.22023-3-kai.vehmanen@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>