dt-bindings: PCI: Add Renesas RZ/G3S PCIe controller binding

dt-bindings: PCI: Add Renesas RZ/G3S PCIe controller binding

The PCIe IP available on the Renesas RZ/G3S complies with the PCI Express
Base Specification 4.0. It is designed for root complex applications and
features a single-lane (x1) implementation. Add binding documentation for
it.

Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20251119143523.977085-2-claudiu.beznea.uj@bp.renesas.com