hw/misc/stm32l4x5_rcc: Implement STM32L4x5_RCC skeleton

hw/misc/stm32l4x5_rcc: Implement STM32L4x5_RCC skeleton

Add the necessary files to add a simple RCC implementation with just
reads from and writes to registers. Also instantiate the RCC in the
STM32L4x5_SoC. It is needed for accurate emulation of all the SoC
clocks and timers.

Signed-off-by: Arnaud Minier <arnaud.minier@telecom-paris.fr>
Signed-off-by: Inès Varhol <ines.varhol@telecom-paris.fr>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20240303140643.81957-2-arnaud.minier@telecom-paris.fr
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>