dt-bindings: arm: Convert Calxeda L2 cache controller to json-schema

Convert the L2-ECC controller binding to DT schema format using
json-schema.
This is indented to be just used for error reporting.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Rob Herring <robh@kernel.org>