hw/misc/stm32l4x5_rcc: Add an internal PLL Clock object

hw/misc/stm32l4x5_rcc: Add an internal PLL Clock object

This object represents the PLLs and their channels. The PLLs allow for a
more fine-grained control of the clocks frequency.

The migration handling is based on hw/misc/zynq_sclr.c.
Three phase reset will be handled in a later commit.

Signed-off-by: Arnaud Minier <arnaud.minier@telecom-paris.fr>
Signed-off-by: Inès Varhol <ines.varhol@telecom-paris.fr>
Message-id: 20240303140643.81957-4-arnaud.minier@telecom-paris.fr
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>