rocker: introduce worlds infrastructure

This is another step on the way to per-world clean cut. Introduce world
ops hooks which each world can implement in world-specific way.
Also introduce world infrastructure along with OF-DPA world stub.

Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>