ARM: dts: stm32: use right pinctrl compatible for stm32f469

Currently, same stm32f429-pinctrl driver is used for stm32f429 and
stm32f469. As pin map is different between those 2 MCUs,
a stm32f469-pinctrl driver has been recently added.
This patch
 -allows to use stm32f469-pinctrl driver for stm32f469 boards
 -reworks stm32 devicetree files to fit with stm32f429 / stm32f469

In the same time it fixes an issue when only MACH_STM32F469 flag is
selected in menuconfig.

Fixes: d28bcd53 ("ARM: stm32: Introduce MACH_STM32F469 flag")
Reported-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>