drivers/pci/layerscape: Add EP mode support

drivers/pci/layerscape: Add EP mode support

The patch will initialize PCIe controller on EP mode
1. Setup bar:
   bar0 32bit 4K for specific configuration
   bar1 32bit 8K for MSIX
   bar2 64bit 4K for descriptor of memory
   bar4 64bit 1M for DMA memory test
2. Setup iATU:
   iATU inbound 0-3 to map bar transaction to memory address
   started at CONFIG_SYS_PCI_EP_MEMORY_BASE
   iATU outbound 0 to map 4G memory space

Signed-off-by: Minghuan Lian <Minghuan.Lian@freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>