Generic VIVPT data cache; a step towards a fix for #23

This is the hybrid VIVT+VIPT cache I have been meaning to try for a
near-decade.  The idea is to get close to the minimal overhead of a
VIVT cache, but without the software exposed effect of aliases.  The
price for this is primarily twice the tags and a more complicated
implementation.

I wrote the initial implementation and had Claude.ai review the code
(~ 6 iteration) and made it write test bench (~ 7 iterations).

This still need to be integrated to show an effect.

Author: tommythorn