Rather than having the autobuild know about the particular variants, have
the mpconfigboard.mk describe them and make autobuild discover them
automatically.
Adds a "query-variants" target to stm32/Makefile to allow the set of
possible variants to be queried.
Removes pybv3 from the autobuild as this isn't use by the downloads page.
Signed-off-by: Jim Mussared <jim.mussared@gmail.com>
Any board with a board.json file will be built. Additional variants for
certain pyboards will also be built by the explicit build-stm32-extra.sh
script. Both .dfu and .hex files will be made available.
Also build boards in a sorted order, and don't stop building if a single
board fails.
Signed-off-by: Damien George <damien@micropython.org>