PCI: layerscape: Add class code and multifunction fixups for ls1021a

The current code depends on class code and multifunction fixups done by the
bootloader.  Perform these fixups in ls1021_pcie_host_init() to remove this
dependency.

Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Roy Zang <tie-fei.zang@freescale.com>