dt-bindings: pci: rcar-pci-ep: Document r8a7795

Document the support for R-Car PCIe EP on R8A7795 SoC device.

Signed-off-by: Yuya Hamamachi <yuya.hamamachi.sx@renesas.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Krzysztof Wilczyński <kw@linux.com>
Link: https://lore.kernel.org/r/e4acfe90021e45658e82ed042746707ace208a93.1635337518.git.geert+renesas@glider.be


Signed-off-by: Rob Herring <robh@kernel.org>