[Libre-soc-dev] versa_ecp5.py paramaterization update

[Cole Poirier]

Hi Luke,

Ended up using argparse (was surprised how easy it was) to add the
commandline arg `--fpga` to litex/florent/versa_ecp5.py, defaults to
versa_ecp5, other option is ulx3s85f. Tested works like it did before.
Committed and pushed.

I think in light of this experience with argparse, and how heavily it
is used in code already (I know it's because of litex), I'd like to
use argparse instead of getopt. Is that ok with you?

Cole