Figured out where the prom console routines are on KA60 and how to invoke

Figured out where the prom console routines are on KA60 and how to invoke
them, thanks to old ultrix bootblocks lying around.
Also, enable M-Bus clock on the I/O slot IOCSR, this unstucks the cpu
clocks (which really are implemented on the SSC on the I/O module, but
need to be controlled via the cpu's ``internal'' processor registers...)