pinctrl: renesas: rzt2h: Add pin configuration support

pinctrl: renesas: rzt2h: Add pin configuration support

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

Implement pinconf_ops to allow reading and updating these properties
through the generic pin configuration framework. The implementation
supports bias-disable, bias-pull-up, bias-pull-down,
input-schmitt-enable, slew-rate, and drive-strength-microamp.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://patch.msgid.link/20260319141515.2053556-3-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>