drivers/clock_control: stm32: Add stm32u5 support

Add clock_control driver to stm32u5 support.
For this series, now deprecated STM32 clock Kconfig symbols
are not added.
Due to a divergence in MSI clock definition, PLL1 use
instead of PLL and lack of sufficient abstraction abstraction
for these a dedicated file has been added.
This should be reshuffled:
- once a better abstraction is provided by LL API for these
- when some stm32 clock control driver rework will be done
after complete removal of Kconfig STM32 clock symbols.

Tested in MSI, HSI, PLL based HSI and PLL based MSI.
Not tested on HSE due to lack of compatible hardware.

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