soc/arm: stm32: use _INST_ namespace in devicetree pinctrl helpers

Current set of helpers provided for STM32 pinctrl devicetree are
using device instance as input.
In order to prepare for next version that will take node identifier
as input, change existing set of macros using _INST_ namespace.

Additionally rename NODE_ID_FROM_PINCTRL to
ST_STM32_DT_INST_NODE_ID_FROM_PINCTRL.

Finally update existing macros users to this new name scheme.

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