of: Drop cpu.h include from of_device.h

Now that all users which had an implicit dependency on cpu.h have been
fixed. the cpu.h include can be dropped from of_device.h

Link: https://lore.kernel.org/r/20230329-dt-cpu-header-cleanups-v1-19-581e2605fe47@kernel.org


Signed-off-by: Rob Herring <robh@kernel.org>