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>

Conflicts:
	drivers/Makefile
exfat: AIO Optimization compatibility fixup

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

Conflicts:
	fs/Kconfig
fs:exfat: move exfat driver from /drivers to /fs and add choice to Kconfig