pkg/fatfs: integrate diskio layer to mtd interface

Makefile.dep

pkg/fatfs/Makefile.dep

pkg/fatfs/Makefile.include

pkg/fatfs/fatfs_diskio/common/fatfs_diskio_common.c

pkg/fatfs/fatfs_diskio/mtd/Makefile

pkg/fatfs/fatfs_diskio/mtd/include/fatfs_diskio_mtd.h

pkg/fatfs/fatfs_diskio/mtd/mtd_diskio.c

pkg/fatfs/fatfs_diskio/native/Makefile

pkg/fatfs/fatfs_diskio/native/native_diskio.c

pkg/fatfs/fatfs_diskio/sdcard_spi/Makefile

pkg/fatfs/fatfs_vfs/fatfs_vfs.c

sys/include/fs/fatfs.h

tests/pkg_fatfs/Makefile

tests/pkg_fatfs/README.md

tests/pkg_fatfs/main.c

tests/pkg_fatfs_vfs/Makefile

tests/pkg_fatfs_vfs/README.md

tests/pkg_fatfs_vfs/create_fat_image_file.sh

tests/pkg_fatfs_vfs/main.c

tests/pkg_fatfs_vfs/tests/01-run.py