of: kill struct of_device

Now that the device tree node pointer has been moved out of struct
of_device and into the common struct device, there isn't anything
unique about of_device anymore.  In fact, there isn't much need
for a separate of_bus when all busses have access to OF style
probing.

arch/powerpc and arch/microblaze are moving away from using the of_bus
and using the regular platform bus instead for mmio devices.  This
patch makes of_device the same as platform_device as a stepping stone
in migrating of_platform_drivers over to the platform bus.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: David S. Miller <davem@davemloft.net>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>