dt-bindings: memory-controllers: Convert Calxeda DDR to json-schema

Convert the Calxeda DDR memory controller binding to DT schema format
using json-schema.
Although this technically covers the whole DRAM controller, the
intention to use it only for error reporting and mapping fault addresses
to DRAM chips.

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