Add support for the Micrel KSZ8081 ethernet PHY.

The only thing this phy needs that the ukphy driver doesn't provide is
that the value in the proprietary Phy Control 2 Register must be saved
before doing a soft reset and restored afterwards. Most modern phys have
"sticky bits" for low-level config that survive a reset, but on this one
the values in all registers go back to defaults, wiping out any board-
specific config set up by the bootloader/bios/whatever.