dt-bindings: fu540: prci: convert PRCI bindings to json-schema

FU540-C000 SoC from SiFive has a PRCI block, here we convert
the device tree bindings from txt to YAML.

Signed-off-by: Sagar Kadam <sagar.kadam@sifive.com>
Link: https://lore.kernel.org/r/1601393531-2402-2-git-send-email-sagar.kadam@sifive.com


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