PCI: Add pci_assign_resource_fixed -- allow fixed address assignments

On some embedded systems the PCI address for hotplug devices are not only
known a priori but are required to be at a given PCI address for other
master in the system to be able to access.

An example of such a system would be an FPGA which is setup from user space
after the system has booted.  The FPGA may be access by DSPs in the system
and those DSPs expect the FPGA at a fixed PCI address.

Added pci_assign_resource_fixed() as a way to allow assignment of the PCI
devices's BARs at fixed PCI addresses.
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>