into sys/dev/dec and split into a clockfns layer and a "middle" layer
for other DEC systems which use mcclocks with each onchip byte
register padded out to a 32-bit word.
Clone alpha/alpha/mcclock (also duplicated in pmax port) into
sys/dev/dec, and ifdef for default clockrates on pmax and alpha.
Use new machinery on pmax for ibus,ioasic attached mcclocks.
