powerpc: Create pci_controller_ops.dma_bus_setup and shim

Add pci_controller_ops.dma_bus_setup, shadowing ppc_md.pci_dma_bus_setup.
Add a shim, and changes the callsites to use the shim.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>