drivers/exfat: add Samsung's open source exFat module version 1.2.4

Signed-off-by: Paul Reioux <reioux@gmail.com>

drivers/Makefile: add exFat support

Signed-off-by: Paul Reioux <reioux@gmail.com>

exfat: AIO Optimization compatibility fixup

Signed-off-by: Paul Reioux <reioux@gmail.com>