dt-bindings: Drop kernel copy of common reserved-memory bindings

The common reserved-memory bindings have recently been copied from the
kernel tree into dtschema. The preference is to host common, stable
bindings in dtschema. As reserved-memory is documented in the DT Spec,
it meets the criteria.

The v2023.09 version of dtschema is what contains the reserved-memory
schemas we depend on, so bump the minimum version to that. Otherwise,
references to these schemas will generate errors.

Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20231013200851.347042-1-robh@kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>