regmap: kunit: Introduce struct for test case parameters

Add a struct regmap_test_param and use it for all test cases
instead of passing various different types of param object
depending on the test case.

This makes it much easier and cleaner to expand what can be
parameterized.
Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Link: https://msgid.link/r/20240408144600.230848-4-rf@opensource.cirrus.comSigned-off-by: Mark Brown <broonie@kernel.org>