[libre-riscv-dev] spike-sv non-default element widths

[lkcl]

okay!  at last, retrieving / storing to registers (integer only at the
moment) actually works, with a c.mv preliminary test, on bit-widths of
default (xlen), 8, 16 and 32.  i've yet to put in sign/zero-extension,
that's going to be interesting / tricky and i may need some help.

l.