MFC r205003:

MFC r205003:
  Revert r204992 and just wrap it all in ifdef INVARIANTS to fix the debug
  and non-debug cases

MFC r204992:
  fixes a compile error if INVARIANTS is disabled.

  Pointy hat to: me
  Submitted by: Michael Butler <imb at protected-networks dot net>

MFC r204983:
  Fix build breakage introduced in r204922.

MFC r204923:
  uses KOBJMETHOD_END macro to indicate the end of method table.

  Submitted by: yongari

MFC r204922:
  o uses bus accessor macros to read values from ivar so no more values
    are referenced directly from ivar pointer.  It's to do like what other
    buses do. [1]
  o changes exported prototypes.  It doesn't use struct siba_* structures
    anymore that instead of it it uses only device_t.
  o removes duplicate code and debug messages.
  o style(9)

  Pointed out by:        imp [1]

git-svn-id: svn://svn.freebsd.org/base/stable/8@206969 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f