Currently only tested boards provide the feature riotboot.
Potentially all boards embeding a cortex-m0+/3/4/7 are
able to have riotboot as a feature, but other dependencies
need to be met, e.g. usage of cortexm.ld linker script,
double initialisation of cpu_init(), etc. See doc in
bootloaders/riotboot.
The file always exist so no need to do '-include'.
Replaced using:
sed -i 's|-\(include $(RIOTCPU)/.*/Makefile.features\)|\1|' \
$(git grep -l '$(RIOTCPU)/.*/Makefile.features' boards)
