Experimental merge of of_platform_bus_type with platform_bus_type.

[Grant Likely]

Hi Timur and Michal,

If you guys are interested, my experimental branch on git.secretlab.ca
not has the of_device merge with platform device, and the removal of
of_platform_bus_type.  If you've got some time, I'd love to have a
sanity test on mpc8xxx and microblaze.

Thanks,
g.