rst was not directly assigned/used on reset_less clock domains, so reset_less
property was not really useful. With the changes on stream.CDC, having a rst
(Even fixed at 0) is now mandatory on clock domains involved in the CDC, so this
also fixes targets.
CPU parameters are now selectively exposed to the user:
./digilent_arty.py --cpu-type=vexriscv_smp --help will show VexRiscv-SMP parameters.
./digilent_arty.py --cpu-type=naxriscv --help will show NaxRiscv parameters.
Florent Kermarrec
Andrew Gillham