MFC: 185750
- According to the corresponding Linux, NetBSD and OpenSolaris drivers, there should be a 1us delay after every write when bit-banging the MII. Also insert barriers in order to ensure the intended ordering. These changes hopefully will solve the bus wedging occasionally experienced with DM9102A since r182461.
- Deobfuscate dc_mii_readreg() a bit.
Approved by: re (kib)