driver/fsl_pci: Add fsl_pci_init_port function to initialize a PCI controller

fsl_pci_init_port can be called from board specific PCI initialization
routines to setup the PCI (or PCIe) controller.  This will reduce code
redundancy in most of the 85xx/86xx FSL board ports that setup PCI.

Signed-off-by: Poonam Aggrwal <poonam.aggrwal@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>