powernv/pci: Remove dma_dev_setup() for NPU PHBs

The pnv_pci_dma_dev_setup() only does something when:

1) There PHB contains VFs, or
2) The PHB defines a dma_dev_setup() callback in the pnv_phb structure.

Neither is true for NPU PHBs so there's no reason to set the callback.

Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200110070207.439-3-oohall@gmail.com