of/device: Replace of_device with platform_device in includes and core code

of_device is currently just an #define alias to platform_device until it
gets removed entirely.  This patch removes references to it from the
include directories and the core drivers/of code.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: David S. Miller <davem@davemloft.net>