PCI: layerscape: Remove unused fields from struct ls_pcie

Removed unused node, dev, and bus fields from struct ls_pcie.

[bhelgaas: split into separate patch]
Signed-off-by: Minghuan Lian <Minghuan.Lian@freescale.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>