PCI: Move ecam.h to linux/include/pci-ecam.h

This header will be used from arch/arm64 for ACPI PCI implementation so it
needs to be moved out of drivers/pci.

Update users of the header file to use the new name.  No functional
changes.

Signed-off-by: Jayachandran C <jchandra@broadcom.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>