[Libre-soc-dev] change sv ld/st to allow non-zero immediates for unit-strided load/store

[lkcl]

hard-no - non-negotiable - on making specific registers "special".
i don't care what the consequences are: enough is enough.  it's
been two years now.  this should have been brought up and
discussed *at least* one year ago.

there are an alarmingly high number of modes as it is, LDST has
undergone approximately seven major design revisions, each time
losing one mode over another, making several unsatisfactory
compromises.

a better option is to propose new scalar ld/st instructions
within the EXT2xx group (even if it requires 8-10 Major EXT2xx
POs to do so) and to even go so far as to define a second
RM Mode table if needed, rather than attempt to jam more
modes into RM.LDST_IMM (and damage it or make further
unsatisfactory compromises as a result).

l.