dt-bindings: clock: brcm, iproc-clocks: convert to the json-schema

This helps validating DTS files.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>