[backport v3.1-branch] drivers: gpio: stm32: Apply GPIOG specific code to U5 series

[erwango]

In STM32U5 as well it is required to enable VDD before use. Difference is that U5 enables this under PWR_SVMCR_IO2SV flag.

Note: Solution slightly differs from the fix done in main branch as a #ifdef CONFIG_SOC_SERIES_STM32U5X was preferred over a fix in hal in order to avoid maintaining a specific v3.1 branch on hal_stm32 module.

Fixes https://github.com/zephyrproject-rtos/zephyr/issues/50158