net: ti/cpsw: Add explicit platform_device.h and of_platform.h includes

TI CPSW uses of_platform_* functions which are declared in of_platform.h.
of_platform.h gets implicitly included by of_device.h, but that is going
to be removed soon. Nothing else depends on of_device.h so it can be
dropped. of_platform.h also implicitly includes platform_device.h, so
add an explicit include for it, too.

Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>