pci/layerscape: add support for LS1043A PCIe LUT register access

The endian and base address of PEX LUT register region is different
between Chassis 2 and Chassis 3, so move the base address definition
to chassis specific header file and add pex_lut_* functions to access
LUT register.

Signed-off-by: Mingkai Hu <Mingkai.Hu@freescale.com>
Signed-off-by: Gong Qianyu <Qianyu.Gong@freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>