drivers: pinctrl: stm32: Kconfig: add missing dependency

Add a missing `PINCTRL_STM32` dependency
for `PINCTRL_STM32_REMAP_INIT_PRIORITY` option to use
that option only when STM32 pinctrl driver is being used.

Signed-off-by: Bartosz Bilas <bartosz.bilas@hotmail.com>