CFT: Overhauled CPSW driver for BeagleBone

I've made some progress reworking the CPSW driver for
BeagleBone and would appreciate any feedback:

  https://github.com/kientzle/cpsw

I believe I've resolved the most pressing stability
problems; the driver properly survives cables
being unplugged and replugged, modules being
loaded and unloaded while the network is
busy, etc.

The most obvious remaining issue:  TX interrupts
still just stop occasionally.  But the watchdog now
consistently detects and resets everything within
a few seconds, so that's much less of a headache.

I hope to commit this to FreeBSD-CURRENT within
the week.

Tim