[libre-riscv-dev] morphing 6600 code to use power decoder

[Luke Kenneth Casson Leighton]

https://groups.google.com/forum/#!topic/comp.arch/qeMsE7UxvlI
https://libre-soc.org/3d_gpu/architecture/6600scoreboard/
https://www.youtube.com/watch?v=ohHbWRLDCfs

this is quite a significant core change to the 6600 scoreboard engine,
so i'm soliciting outside help in reviewing it.  ironically (and very
much to the point) i realised an error towards the end of the
description.

l.