boards: adapted to HWRNG changes

boards/airfy-beacon/Makefile.features

boards/airfy-beacon/include/periph_conf.h

boards/arduino-due/Makefile.features

boards/arduino-due/include/periph_conf.h

boards/cc2538dk/Makefile.features

boards/cc2538dk/include/periph_conf.h

boards/frdm-k64f/Makefile.features

boards/frdm-k64f/include/periph_conf.h

boards/msbiot/Makefile.features

boards/msbiot/include/periph_conf.h

boards/mulle/Makefile.features

boards/mulle/include/periph_conf.h

boards/native/Makefile.features

boards/nrf51dongle/Makefile.features

boards/nrf51dongle/include/periph_conf.h

boards/nrf52dk/Makefile.features

boards/nrf52dk/include/periph_conf.h

boards/nrf6310/Makefile.features

boards/nrf6310/include/periph_conf.h

boards/openmote-cc2538/Makefile.features