powerpc/fsl-pci: Set relaxed ordering on prefetchable ranges

Provides a small speedup when accessing pefetchable ranges.  To indicate
that a memory range is prefetchable, mark it in the dts file with 42000000
instead of 02000000.

A powepc pci_controller is allowed three memory ranges, any of which may be
prefetchable.  However, the PCI-PCI bridge configuration space only has one
field for "non-prefetchable memory behind bridge", which has a 32 bit
address, and one field for "prefetchable memory behind bridge", which may
have a 64 bit address.  These are PCI bus addresses, not CPU physical
addresses.

So really you're only allowed one memory range of each type.  And if you
want the range at a PCI address above 32 bits you must make it
prefetchable.

Signed-off-by: Trent Piepho <tpiepho@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>