Add a helper routine to conditionally modify the start address of a

Add a helper routine to conditionally modify the start address of a
resource allocation from an x86 Host-PCI bridge driver so that it can be
reused by the ACPI Host-PCI bridge driver (and eventually the MPTable
Host-PCI bridge driver) instead of duplicating the same logic.  Note that
this means that hw.acpi.host_mem_start is now replaced with the
hw.pci.host_mem_start tunable that was already used in the non-ACPI case.
This also removes hw.acpi.host_mem_start on ia64 where it was not
applicable (the implementation was very x86-specific).

While here, adjust the logic to apply the new start address on any
"wildcard" allocation even if that allocation comes from a subset of
the allowable address range.

Reviewed by:	imp (1)