pinctrl: stm32: Add STM32F469 MCU support

This patch which adds STM32F469 pinctrl and GPIO support, relies on the
generic STM32 pinctrl driver.

Signed-off-by: Alexandre TORGUE <alexandre.torgue@st.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>