If Enhanced Allocation is not used, we can't allocate any random
range. All internal devices have hardcoded place where they can
be located within PCI address space. Fortunately, we can read
this value from BAR.
Obtained from: Semihalf
Sponsored by: Cavium
Approved by: cognet (mentor)
Reviewed by: zbb
Differential revision: https://reviews.freebsd.org/D5455