Merge pull request #9074 from haukepetersen/opt_nrf5x_nrfminfeature

boards/airfy-beacon/Makefile.features

boards/airfy-beacon/include/periph_conf.h

boards/calliope-mini/Makefile.features

boards/calliope-mini/include/periph_conf.h

boards/common/nrf52xxxdk/Makefile.features

boards/microbit/Makefile.features

boards/microbit/include/periph_conf.h

boards/nrf51dongle/Makefile.features

boards/nrf51dongle/include/periph_conf.h

boards/nrf6310/Makefile.features

boards/nrf6310/include/periph_conf.h

boards/ruuvitag/Makefile.features

boards/thingy52/Makefile.features

boards/yunjia-nrf51822/Makefile.features

boards/yunjia-nrf51822/include/periph_conf.h

cpu/nrf5x_common/Makefile.features