ohci: Add support for OHCI controller on the of_platform bus

PPC embedded systems can have a ohci controller builtin. In the
new model, it will end up as a driver on the of_platform bus,
this patches takes care of them.

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>