Added support for PCI prefetchable region and BARs

If a host controller sets up a region as prefetchable and
a device's BAR denotes it as prefetchable, allocate the
BAR into the prefetch region.

If a BAR is prefetchable and no prefetchable region has
been setup by the controller we fall back to allocating
the BAR into the normally memory region.
Patch by Kumar Gala 11 Jan 2006