For example, some BIOS for AMD SB600 south bridge may map HPET MMIO base
address as a memory BAR for SMBus controller depending on a PM register
configuration. Before r231161 (and r232086, subsequent MFC to stable/9),
it was not fatal but hpet(4) just failed to attach. Since we probe and
attach HPET earlier than PCI devices now, it caused unfortunate hard lockup.
With this patch, it does not hang any more and HPET works at the same time.
Clean up some style nits while I am in the neighborhood.
PR: kern/165647
Reviewed by: jhb
MFC after: 3 days
96ec27d42b