Add a KUnit test for cirrus_scodec_get_speaker_id(). It is impractical
to have enough hardware with every possible permutation of speaker id.
So use a test harness to test all theoretically supported options.

The test harness consists of:
- a mock GPIO controller.
- a mock struct device to represent the scodec driver
- software nodes to provide the fwnode info that would normally come
  from ACPI.
Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20230918095129.440-3-rf@opensource.cirrus.comSigned-off-by: Takashi Iwai <tiwai@suse.de>