dt-bindings: PCI: pci-rcar-gen2: Convert bindings to json-schema

Convert Renesas PCI bridge bindings documentation to json-schema.

Link: https://lore.kernel.org/r/20220520094155.313784-2-herve.codina@bootlin.com


Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>