ppc/85xx/pci: fsl_pci_init: pcie agent mode support

Originally written by Jason Jin and Mingkai Hu for mpc8536.

When QorIQ based board is configured as a PCIe agent, then unlock/enable
inbound PCI configuration cycles and init a 4K inbound memory window;
so that a PCIe host can access the PCIe agents SDRAM at address 0x0

* Supported in fsl_pci_init_port() after adding pcie_ep as a param
* Revamped copyright in drivers/pci/fsl_pci_init.c
* Mods in 85xx based board specific pci init after this change

Signed-off-by: Vivek Mahajan <vivek.mahajan@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>