Merge pull request #8585 from basilfx/feature/efm32_stk3600_v2

boards/stk3600/Makefile

boards/stk3600/Makefile.dep

boards/stk3600/Makefile.features

boards/stk3600/Makefile.include

boards/stk3600/board.c

boards/stk3600/include/board.h

boards/stk3600/include/gpio_params.h

boards/stk3600/include/periph_conf.h

cpu/efm32/families/efm32lg/Makefile

cpu/efm32/families/efm32lg/cpus.txt

cpu/efm32/families/efm32lg/include/vendor/efm32lg990f256.h

cpu/efm32/families/efm32lg/include/vendor/efm32lg_acmp.h

cpu/efm32/families/efm32lg/include/vendor/efm32lg_adc.h

cpu/efm32/families/efm32lg/include/vendor/efm32lg_aes.h

cpu/efm32/families/efm32lg/include/vendor/efm32lg_af_pins.h

cpu/efm32/families/efm32lg/include/vendor/efm32lg_af_ports.h

cpu/efm32/families/efm32lg/include/vendor/efm32lg_burtc.h

...efm32/families/efm32lg/include/vendor/efm32lg_burtc_ret.h

...efm32/families/efm32lg/include/vendor/efm32lg_calibrate.h

cpu/efm32/families/efm32lg/include/vendor/efm32lg_cmu.h