Using MICROPY_FATFS_EXFAT. Enabling this has licensing implications; see https://www.microsoft.com/en-us/legal/intellectualproperty/mtl/exfat-licensing.aspx
From https://github.com/micropython/oofatfs, branch work-R0.12b, commit a346ccec123c2e4d887e2751d64156208d03bff4.