[libre-riscv-dev] sv opcodes categorisation table

[Luke Kenneth Casson Leighton]

https://libre-riscv.org/simple_v_extension/opcodes/

ok so this is a table which begins to categorise the type of
"parallelism/for-looping" that each SV-augmented instruction falls
into.  i'll reorder them over time so that the instructions in each
category are grouped together.

still undecided is what to do with CSRR*, as it may be advantageous to
be able to load/store multiple consecutive CSRs, particularly in
context-switches.  however, get that wrong and it may be difficult to
enable or disable SV!

l.