Merge pull request #4780 from haukepetersen/opt_periph_spi2

boards/airfy-beacon/include/periph_conf.h

boards/arduino-due/include/periph_conf.h

boards/arduino-due/include/sdcard_spi_params.h

boards/arduino-due/include/w5100_params.h

boards/arduino-zero/include/periph_conf.h

boards/cc2538dk/include/periph_conf.h

boards/fox/include/board.h

boards/fox/include/periph_conf.h

boards/frdm-k64f/include/periph_conf.h

boards/iotlab-a8-m3/include/periph_conf.h

boards/iotlab-common/include/board_common.h

boards/iotlab-common/include/periph_conf_common.h

boards/iotlab-m3/include/board.h

boards/iotlab-m3/include/periph_conf.h

boards/limifrog-v1/include/periph_conf.h

boards/maple-mini/include/periph_conf.h

boards/msb-430/Makefile.features

boards/msb-430/include/periph_conf.h

boards/msb-430h/include/periph_conf.h

boards/msba2/include/periph_conf.h