hw/misc: Create STM32L4x5 SYSCFG clock

hw/misc: Create STM32L4x5 SYSCFG clock

This commit creates a clock in STM32L4x5 SYSCFG and wires it up to the
corresponding clock from STM32L4x5 RCC.

Signed-off-by: Inès Varhol <ines.varhol@telecom-paris.fr>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Luc Michel <luc@lmichel.fr>
Message-id: 20241003081105.40836-2-ines.varhol@telecom-paris.fr
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>