ARM: kirkwood: switch to using mvebu mbus

ARM: kirkwood: switch to using mvebu mbus

The mvebu mbus code already had most of the support required for
kirkwood. The only difference is that unlike the other mvebu targets
kirkwood doesn't have a bridge control block so the code related to
managing that needs to be compiled out.

Signed-off-by: Chris Packham <judge.packham@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Signed-off-by: Stefan Roese <sr@denx.de>