dt-bindings: pinctrl: renesas,r9a09g077: Document pin configuration properties

dt-bindings: pinctrl: renesas,r9a09g077: Document pin configuration properties

Document the pin configuration properties supported by the RZ/T2H
pinctrl driver.

The RZ/T2H SoC allows configuring several electrical characteristics
through the DRCTLm (I/O Buffer Function Switching) registers. These
registers control drive strength, bias configuration, Schmitt trigger
input, and output slew rate.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://patch.msgid.link/20260319141515.2053556-2-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>