This change allows drivers (or any module for that matter) to provide
features. This is e.g. useful if a board does not have a transceiver,
but your application uses `USEMODULE += some_driver`, which implements
the transceiver interface.
The line `FEATURES_PROVIDED += some_feature` should go to the guarded
block in `{sys,drivers}/Makefile.include`.
Sometimes boards/*/Makefile.include (e. g. in case of the msba2) gets included
twice somehow, leading the TERMFLAG to be set twice and faulty. This
fixes that.