of: Stop circularly including of_device.h and of_platform.h

The DT of_device.h and of_platform.h headers date back to the separate
of_platform_bus_type before it was merged into the regular platform bus.
As part of that merge prepping Arm DT support 13 years ago, they
"temporarily" include each other. The headers also include
platform_device.h and of.h. The result was lots of drivers relied on
these implicit includes.

Now the entire tree has been fixed over the last couple of cycles to
explicitly include the necessary headers instead of relying on
of_device.h and/or of_platform.h implicit includes, so the implicit and
circular includes can finally be removed.

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