Merge pull request #6223 from haukepetersen/opt_samxyz21_structure

boards/arduino-zero/Makefile.include

boards/samr21-xpro/Makefile.include

boards/sodaq-autonomo/Makefile.include

cpu/sam0_common/Makefile

cpu/sam0_common/Makefile.include

cpu/sam0_common/include/cmsis/samd21/README.md

cpu/sam0_common/include/cmsis/samd21/include/component/ac.h

cpu/sam0_common/include/cmsis/samd21/include/component/adc.h

cpu/sam0_common/include/cmsis/samd21/include/component/dac.h

...sam0_common/include/cmsis/samd21/include/component/dmac.h

cpu/sam0_common/include/cmsis/samd21/include/component/dsu.h

cpu/sam0_common/include/cmsis/samd21/include/component/eic.h

...am0_common/include/cmsis/samd21/include/component/evsys.h

...sam0_common/include/cmsis/samd21/include/component/gclk.h

..._common/include/cmsis/samd21/include/component/hmatrixb.h

cpu/sam0_common/include/cmsis/samd21/include/component/i2s.h

cpu/sam0_common/include/cmsis/samd21/include/component/mtb.h

...0_common/include/cmsis/samd21/include/component/nvmctrl.h

cpu/sam0_common/include/cmsis/samd21/include/component/pac.h

cpu/sam0_common/include/cmsis/samd21/include/component/pm.h