MFC: r260050, r261528

MFC: r260050, r261528

- Switch to using the common MII bitbang'ing code instead of duplicating it.
- Based on lessons learnt with dc(4) (see r185750), add bus space barriers to
  the MII bitbang read and write functions as well as to instances of page
  switching.
- Add missing locking to ed_ifmedia_{upd,sts}().
- Canonicalize some messages.
- Based on actual functionality, ED_TC5299J_MII_DIROUT should be rather named
  ED_TC5299J_MII_DIRIN.
- Remove unused headers.
- Use DEVMETHOD_END.
- Use NULL instead of 0 for pointers.

git-svn-id: svn://svn.freebsd.org/base/stable/10@264942 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f