Add a new Core Xeon CPU and an older Pentium Pro model to the bus clock detection.  Also improve the error message in case of an unknown CPU, so we can more easily see what needs to be added.
Add a new Core Xeon CPU and an older Pentium Pro model to the bus
clock detection.  Also improve the error message in case of an unknown
CPU, so we can more easily see what needs to be added.

Tested by brad@ and others.

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars