moving the typedef of bus_space_tag_t from sys/sparc64/include/bus.h
to sys/sparc64/include/_bus.h. This brings sparc64 in sync with the
other platforms and fixes the compilation of drivers which include
<sys/rman.h> before <machine/bus.h> after sys/sys/rman.h rev. 1.34.
- Remove the definition of bus_type_t from sys/sparc64/include/_bus.h
as it's unused since sys/sparc64/include/bus.h rev. 1.6 and
sys/sparc64/sparc64/bus_machdep.c rev. 1.3.
- Remove some pointless comments.
ab098c4184