arm64: dts: renesas: rzg2l-smarc: Enable GPT on carrier board

The GPT4 IOs are available on the carrier board's PMOD0 connector (J1).
Enable the GPT on the carrier board by adding the GPT pinmux and node on
the carrier board dtsi file.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/20250424054050.28310-4-biju.das.jz@bp.renesas.com


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