hw/pci-host: Use register definitions from PCI standard

hw/pci-host: Use register definitions from PCI standard

No need to document magic values when the definition names
from "standard-headers/linux/pci_regs.h" are self-explicit.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20230105173702.56610-1-philmd@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: BALATON Zoltan <balaton@eik.bme.hu>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Bernhard Beschow <shentey@gmail.com>