Merge pull request #6072 from MichelRottleuthner/fatfs_testing

pkg/fatfs/Makefile

pkg/fatfs/Makefile.dep

pkg/fatfs/Makefile.fatfs

pkg/fatfs/Makefile.include

pkg/fatfs/fatfs_diskio/common/Makefile

pkg/fatfs/fatfs_diskio/common/fatfs_diskio_common.c

pkg/fatfs/fatfs_diskio/common/include/fatfs_diskio_common.h

pkg/fatfs/fatfs_diskio/native/Makefile

pkg/fatfs/fatfs_diskio/native/native_diskio.c

pkg/fatfs/fatfs_diskio/sdcard_spi/Makefile

pkg/fatfs/fatfs_diskio/sdcard_spi/sdcard_spi_diskio.c

sys/Makefile

tests/pkg_fatfs/Makefile

tests/pkg_fatfs/README.md

tests/pkg_fatfs/main.c