mpc83xx: add "fsl,soc" and "fsl,immr" compatible fixups

device_type = "soc" is being deprecated, newer device trees will use
"fsl,soc" and/or "fsl,immr" for the soc nodes.

This patch also adds clock-frequency property for soc nodes (the same
value as bus-frequency).

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>