tests/qtest/stm32l4x5_rcc-test.c: Add tests for the STM32L4x5_RCC

tests/qtest/stm32l4x5_rcc-test.c: Add tests for the STM32L4x5_RCC

Tests:
- the ability to change the sysclk of the device
- the ability to enable/disable/configure the PLLs
- if the clock multiplexers work
- the register flags and the generation of irqs

Signed-off-by: Arnaud Minier <arnaud.minier@telecom-paris.fr>
Signed-off-by: Inès Varhol <ines.varhol@telecom-paris.fr>
Acked-by: Thomas Huth <thuth@redhat.com>
Message-id: 20240303140643.81957-9-arnaud.minier@telecom-paris.fr
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>