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

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

Add convenience macros for bus_space usage that doesn't require specification
of bus tag+handle.

Instead of
bus_space_write_1(sc->tag, sc->handle, ...)
this macros offer
bus_write_1(sc->resource, ...)

The name+argument transformation is constant and the the macros are
generated (by hand) by the script in tools/bus_macro.sh.