dt-bindings: arm: renesas: Convert 'renesas,prr' to json-schema

Convert Renesas Product Register bindings documentation to json-schema.

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20190908120528.9392-1-horms+renesas@verge.net.au


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>