[libre-riscv-dev] div/mod algorithm written in python

[Luke Kenneth Casson Leighton]

i've added the z-bypass signals (out_do_z, oz) and also the context
(FPPipeContext) - all commented-out - as they need to be initialised
correctly.

these have to go into absolutely every data spec because they're
passed (untouched) right the way through the pipeline.  bit annoying,
but hey.

* the muxid *must* be unmodified.  it's the Reservation Station identifier.

* out_do_z and z are set in SpecialCases.  they must not be touched by
any "processing", as they already contain a result

* ctx.op is where you can completely change the functionality of the
pipeline: it's the ALU "operator", from the instruction decode phase
(or is funct7, or... whatever).

l.