[Simh] XXDP v2

[Bob Supnik]

I did a quick hack and removed the clock from the device list, 
effectively disabling it. With that done, the 11/23 runs XXDP V2 
correctly, with 64KB of memory. I'll add BEVENT DISABLE to formalize this.

So the failing systems are the 03, 04, 05, and 20. Possible common factors:

- no memory management
- no EIS

I tried an 11/03 with EIS and no clock, and it fails, so EIS does not 
appear to be the problem.

I'm now looking for XXDP monitor sources. The failure happens before 
anything is printed, but a listing would still be of great help.

/Bob