PCI: Define macro for Marvell vendor ID

Define PCI_VENDOR_ID_MARVELL_EXT macro for 0x1b4b vendor ID

Signed-off-by: Xiangliang Yu <yuxiangl@marvell.com>
Signed-off-by: Myron Stowe <myron.stowe@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>