tests/drivers/clock_control: stm32u5: Add tests on clock configs

Add a test suite to check various clocks configurations.
Test is based on HAL functions that read clock configuration
from registers.
One test is build only, as there is no available hw to test it today.
Others can be tested on target.

More configurations and test points could be added in future.

Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>