dt-bindings: pinctrl: stm32: Support I/O synchronization parameters

dt-bindings: pinctrl: stm32: Support I/O synchronization parameters

Document the support of the I/O synchronization parameters:
- skew-delay-input-ps;
- skew-delay-output-ps;
- st,io-sync.

Forbid 'skew-delay-input-ps' and 'skew-delay-output-ps' to be both
present on the same pin.
Allow the new properties only with compatibles that support them.
Add an example that uses the new properties.

Co-developed-by: Fabien Dessenne <fabien.dessenne@foss.st.com>
Signed-off-by: Fabien Dessenne <fabien.dessenne@foss.st.com>
Signed-off-by: Antonio Borneo <antonio.borneo@foss.st.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>