PCI: layerscape: Remove ls_pcie_establish_link()

ls_pcie_establish_link() does not do any real operation, except to wait for
the linkup establishment.  In fact, this is not necessary.  Moreover, each
PCIe controller not inserted device will increase the Linux startup time
about 200ms.

Remove ls_pcie_establish_link().

Signed-off-by: Minghuan Lian <Minghuan.Lian@freescale.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>