Takes care of retrieving a FsStorage object for any FAT eMMC BIS partition, mounting it via FatFs and creating a virtual devoptab device that can be used to carry out FS operations. All write operations have been stubbed, disabled or ifdef'd out of the code.
Other changes include:
* cert: update code to use the new BIS storage interface.
* defines: remove BIS_SYSTEM_PARTITION_MOUNT_NAME macro.
* devoptab: slightly improve macros.
* devoptab: add operation table for FatFs devices.
* devoptab: add rodev_fstat().
* devoptab: add devoptabMountFatFsDevice().
* fatfs: update diskio code to use the new BIS storage interface.
* fatfs: update configuration.
* save: update code to use regular C I/O calls instead of FatFs calls.
* tik: update code to use the new BIS storage interface.
* utils: remove eMMC BIS System partition (un)mount code.
