dt-bindings: pincfg-node: Add "output-impedance-ohms" property

On RZ/G2L SoC for Group-B pins, output impedance can be configured. This
patch documents "output-impedance-ohms" property in pincfg-node.yaml so
that other platforms requiring such feature can make use of this property.
Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20211027134509.5036-2-prabhakar.mahadev-lad.rj@bp.renesas.comSigned-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

Documentation/devicetree/bindings/pinctrl/pincfg-node.yaml

@@ -114,6 +114,9 @@ properties:
     description: enable output on a pin without actively driving it
       (such as enabling an output buffer)
 
+  output-impedance-ohms:
+    description: set the output impedance of a pin to at most X ohms
+
   output-low:
     type: boolean
     description: set the pin to output mode with low level