drivers: pinmux: stm32: add support for PA11/12 remap.

STM32G0/F0 SoCs allow to remap PA11/12 to PA9/10. Some boards
were manually configuring this remap. This patch centralizes this
functionality to the pinmux driver, allowing boards to enable the
remap directly in board dts file.

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>
Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>