lib/fatfs: Add support for sector sizes larger than 512 bytes.

If MICROPY_FATFS_MAX_SS is defined to power of 2 value between 1024 and
4096, support for dynamic sector size in FatFs will be enabled.  Note
that FatFs reserves static buffer of MICROPY_FATFS_MAX_SS size for each
filesystem in use, so that value should be set sparingly.

Initial patch provided by @pfalcon.