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.com


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>