Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

There's no need to include all the detauls of struct bus_space_{tag,handle}
in _bus.h when the typedef of the struct pointer will do.

Unbreak the pc98 build by including enough information in the _bus.h
for _bus.h to compile.

Pointy hat to: imp
Breakage noted by: nyan-san

Break out the definition of bus_space_{tag,handle}_t and a few other types
into _bus.h to help with name space polution from including all of bus.h.
In a few days, I'll commit changes to the MI code to take advantage of thse
sepration (after I've made sure that these changes don't break anything in
the main tree, I've tested in my trees, but you never know...).

Suggested by: bde (in 2002 or 2003 I think)
Reviewed in principle by: jhb