dt-bindings: PCI: renesas: Add R-Car Gen4 PCIe Endpoint

dt-bindings: PCI: renesas: Add R-Car Gen4 PCIe Endpoint

Document bindings for Renesas R-Car Gen4 and R-Car S4-8 (R8A779F0)
PCIe endpoint module.

Link: https://lore.kernel.org/linux-pci/20231018085631.1121289-12-yoshihiro.shimoda.uh@renesas.com
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Serge Semin <fancer.lancer@gmail.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Manivannan Sadhasivam <mani@kernel.org>