[libre-riscv-dev] nmutil/* moved to new (separate) repository

[Luke Kenneth Casson Leighton]

updated: https://libre-riscv.org/HDL_workflow/

i've moved nmutil to its own separate repository because it basically
serves the same job as the chisel3 util libraries: it's actually not
dependent on either the ieee754fpu or the soc repository and could be
used independently.

when checking out the latest ieee754fpu it *may* be the case that the
nmutil directory has files left in it, which will interfere with
running python3 setup.py develop in the nmutil repo.  you *may* have
to manually rm -fr the ieee754fpu/src/nmutil subdirectory after a git
pull.

l.