dt-bindings: PCI: rcar: Add device tree support for r8a7742

Add support for r8a7742. The Renesas RZ/G1H (R8A7742) PCIe controller
is identical to the R-Car Gen2 family.

Link: https://lore.kernel.org/r/20200810174156.30880-2-prabhakar.mahadev-lad.rj@bp.renesas.com


Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Chris Paterson <Chris.Paterson2@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Acked-by: Rob Herring <robh@kernel.org>