Add needed uart pinctrl configuration in pinmux node.
This is done thanks to <soc>-pinctrl.dtsi file matching
the <soc>.dtsi files
Populate stm32 f4 based boards dts files with references
to uart pinctrl nodes.
Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>
Erwan Gouriou