fs: add native exFAT support (Samsung OSRC 1.2.4)

http://opensource.samsung.com/reception/receptionSub.do?method=sub&sub=F&searchValue=exfat

Signed-off-by: AndDiSa <anddisa@googlemail.com>
smdk4412: exFAT 1.2.5 (Samsung OSRC)

Change-Id: I299a53095a4777f457cd2e70edde74d8766256cc

Signed-off-by: AndDiSa <anddisa@googlemail.com>