[Libre-soc-dev] LD/ST Elwidth Overrides

[lkcl]

https://libre-soc.org/openpower/sv/ldst/

i've updated the page to take into account the new
mode (Vector Indexed strided) and also removed
ffirst Vector Indexed entirely.  Immediate-mode ffirst remains.

it occurred to me that the Vector-Indexed Strided
mode would also need a signed/unsigned bit
to say if the elwidth-overridden RB was to be treated as +ve or -ve after truncation to 32/16/8 bit.

comments and review welcomed as always.

l.