ASoC: wm8804: Add ACPI support

HID made of either Wolfson/CirrusLogic PCI ID + 8804 identifier.

This helps enumerate the HifiBerry Digi+ HAT boards on the Up2 platform.

The scripts at https://github.com/thesofproject/acpi-scripts

 can be
used to add the ACPI initrd overlays.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>