amd-pstate-ut: Add module parameter to select testcases

amd-pstate-ut: Add module parameter to select testcases

Currently when amd-pstate-ut test module is loaded, it runs all the
tests from amd_pstate_ut_cases[] array.

Add a module parameter named "test_list" that accepts a
comma-delimited list of test names, allowing users to run a
selected subset of tests. When the parameter is omitted or empty, all
tests are run as before.

Signed-off-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Signed-off-by: Mario Limonciello (AMD) <superm1@kernel.org>