dts: bindings: pinctrl: stm32: add SWJ CFG to F1

Adds 'swj-cfg' property to the F1 pinctrl. It is an optional
property that allows to control Serial Wire JTAG
configuration.

Different configurations allow to free certain IO
pins that can be used in remap or standalone.

That replaces previously used Kconfig approach.

Signed-off-by: Georgij Cernysiov <geo.cgv@gmail.com>