soc: st: stm32: common: introduce a wake-up pins driver

Implement GPIO pins configuration as sources for STM32 PWR wake-up pins
behind the scenes exclusively from devicetree information for all series
using the public stm32_pwr_wkup_pin_cfg_gpio() function.
Introduce macros for parsing & storing DT wake-up pins config in C structs.
Introduce user-configurable STM32_WKUP_PINS Kconfig flag.

Signed-off-by: Abderrahmane Jarmouni <abderrahmane.jarmouni-ext@st.com>