dt-bindings: sata: Convert Calxeda SATA controller to json-schema

Convert the Calxeda Highbank SATA controller binding to DT schema format
using json-schema.

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