PCI: keystone: Add support for PCIe EP in AM654x Platforms

Add PCIe EP support for AM654x Platforms in pci-keystone.c

Link: https://lore.kernel.org/linux-pci/20190325093947.32633-15-kishon@ti.com/


Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
[lorenzo.pieralisi@arm.com: made dev_vdbg() call a comment]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>