This is a one controller to many interfaces driver
 cpsw -> mac0 -> ecp0 
         mac1 -> ecp1
plus optionally a virtual interface per port.

This makes it a bit of a frankenstein as some of the NetBSD code zaps the top level CPSW controller when really only dealing with one of the two MACs.

Specifically, this implicates 
 cpsw_start(ifp)
   enables top level CPSW, only call once!
 cpsw_ioctl(ifp)
   boilerplate
 cpsw_init(ifp)
   resets top level CPSW, only call once!
 cpsw_stop(ifp)
   disables top level CPSW, only call once!
 cpsw_watchdog(ifp)
   may call cpsw_init() and cpsw_start() 
 mii_attach(mii)
   need to fudge mii_ifp to be one of two
   should probably use the LIST_FOREACH stuff
 mii_mediachg(mii)
   need to fudge mii_ifp to be one of two
   should probably use the LIST_FOREACH stuff
 mii_down(mii)
   unused
 mii_tick(mii)
   iterates over the two ifps

