Usnure that PCI bus BIS_GET_DMA_TAG() method sees the actual PCI
device which makes the request for dma tag, instead of some descendant
of the PCI device, by creating a pass-through trampoline for vga_pci
and ata_pci buses.

Sponsored by:	The FreeBSD Foundation
Suggested by:	jhb
Discussed with:	jhb, mav
MFC after:	1 week