Revert rr271190, it was based on a misunderstanding.  The problem of
non-existant device<->xref info needs to be handled by creating the info,
which will come in a subsequent commit.
o Remove __unused attribute on variables which actually used
o Unmagic 'configuration done' bit
o Move probe() to place before attach() for better navigation
o Use bus_read_n instead of bus_space_read_n functions

Pointed out by:	andrew
Sponsored by:	DARPA, AFRL
Restore order of interrupt setup. Minor problems can result by
setting up the interrupts too early:

Reviewed by: mav@
Sponsored by: Netflix