This splits the driver into a bus-independant backend, plus bus-specific
frontends. The old pcf(4) (i386/ISA) frontend is now in pcf_isa.c, the
frontend in envctrl.c is for sparc64/Ebus2 (Sun device name: SUNW,envctrl
from Sun E450 machines). More frontends are expected to appear in future.
This is not yet ready for public consumption, but it basically works.
Nicolas will bring over his ISA-specific fixes soon.
Reviewed by: nsouch
