powerpc: Enable device tree support for P5040DS

Add device tree for P5040DS board and enable CONFIG_OF_CONTROL
so that device tree can be compiled.

Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
Reviewed-by: Prabhakar Kushwaha <prabhakar.kushwaha@nxp.com>