dm: core: scan reserved-memory nodes

dm: core: scan reserved-memory nodes

Qualcomm platforms may have drivers that bind to reserved memory nodes
(cmd-db [1] and smem [2]) which are relevant to U-Boot. Include
/reserved-memory in dm_extended_scan() so that these will be handled
correctly.

[1]: https://www.kernel.org/doc/Documentation/devicetree/bindings/reserved-memory/qcom%2Ccmd-db.yaml
[2]: https://www.kernel.org/doc/Documentation/devicetree/bindings/soc/qcom/qcom%2Csmem.yaml

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>