CI: split up Cortex-M4 in two groups

.strider.yml

.travis.yml

boards/ek-lm4f120xl/Makefile.features

boards/f4vi1/Makefile.features

boards/frdm-k64f/Makefile.features

boards/msbiot/Makefile.features

boards/mulle/Makefile.features

boards/nucleo-f303/Makefile.features

boards/nucleo-f334/Makefile.features

boards/nucleo-f401/Makefile.features

boards/pba-d-01-kw2x/Makefile.features

boards/slwstk6220a/Makefile.features

boards/stm32f3discovery/Makefile.features

boards/stm32f4discovery/Makefile.features

dist/tools/drone-scripts/build_and_test.sh

dist/tools/travis-scripts/get-pkg-list.py