ASoC: cs-amp-lib-test: Tests for reading SSIDExV2

ASoC: cs-amp-lib-test: Tests for reading SSIDExV2

Adds test cases for getting a Dell SSIDExV2 string by calling
cs_amp_devm_get_vendor_specific_variant_id().

This is a fairly simple test harness, the redirected call to
cs_amp_get_efi_variable() returns a test string to simulate
reading a string from UEFI. The returned string should be
the second field in the SSIDExV2 string (if valid).

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Link: https://patch.msgid.link/20260121132243.1256019-4-rf@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>