ASoC: cs35l56: KUnit tests for parsing and using onchip GPIOs

ASoC: cs35l56: KUnit tests for parsing and using onchip GPIOs

Add KUnit test cases for:

- cs35l56_process_xu_properties() which reads the onchip GPIO definitions.
- cs35l56_set_fw_name() calls functions to configure and set the GPIOs.
- cs35l56_set_fw_name() saves the ID value in cs35l56_priv.speaker_id.
- cs35l56_set_fw_name() does not overwrite a speaker ID that was already
  found some other way.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Link: https://patch.msgid.link/20260205164838.1611295-4-rf@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>