powerpc/powernv: remove pnv_pci_ioda_pe_single_vendor

This function is completely bogus - the fact that two PCIe devices come
from the same vendor has absolutely nothing to say about the DMA
capabilities and characteristics.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>