dts/st: dtc v1.4.6 warnings: pin-c... node has a reg ... no unit name

To prepare to upcoming dtc v1.4.6, fix warnings in dts files.

This commit addresses the following warning:
Warning (unit_address_vs_reg): Node /soc/pin-controller has a reg
or ranges property, but no unit name

Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>