powerpc: Call dma_debug_add_bus for PCI and VIO buses

The DMA API debug code has hooks to verify all DMA entries have been
freed at time of hot unplug. We need to call dma_debug_add_bus for
this to work.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>