Honor the prefetchable flag in memory BARs by setting the RF_PREFETCHABLE flag when calling bus_alloc_resource() to allocate resources from a parent PCI bridge.  For PCI-PCI bridges this asks the bridge to satisfy the request using the prefetchable memory range rather than the normal memory range.
Honor the prefetchable flag in memory BARs by setting the RF_PREFETCHABLE
flag when calling bus_alloc_resource() to allocate resources from a parent
PCI bridge.  For PCI-PCI bridges this asks the bridge to satisfy the
request using the prefetchable memory range rather than the normal
memory range.

Reviewed by:	imp
Reported by:	scottl
MFC after:	1 week

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