Add mtk_soundcard_pdata platform data for the MediaTek common sound card
probe mechanism, including a driver/soc-specific probe extension (used
for bits that cannot be commonized hence specific to this driver), and
change the probe function to mtk_soundcard_common_probe.
This is also adding the possibility of specifying the links and routing
with the audio-routing property and (x)-dai-link nodes in device trees
to stop hardcoding machine specific links in the card driver assupported
by the common probe function, but support for legacy device trees is
retained with a legacy_probe function, which is used only in case the
new properties are not found.