Introduce PCI_VENDOR/PCI_SUBVENDOR/PCI_SUBDEVICE defines to replace the
constants scattered in the kernel already used to detect QEMU.

They are defined in the QEMU codebase per docs/specs/pci-ids.txt.
Signed-off-by: Robin H. Johnson <robbat2@gentoo.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>