PCI: layerscape: Refactor ls1021_pcie_host_init()

ls1021_pcie_host_init() duplicated the code in the generic
ls_pcie_host_init().  Call ls_pcie_host_init() instead of duplicating the
code.

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>