dt-bindings: clock: renesas: rcar-usb2-clock-sel: Convert bindings to json-schema

Convert Renesas R-Car USB 2.0 clock selector bindings documentation
to json-schema.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1604543524-31482-1-git-send-email-yoshihiro.shimoda.uh@renesas.com


Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>