p509: Apply changes from p500

between
 Cleanup SD Card mounting (805892c8b7ed951cc09c271a238460dbb33a3210)
and
 p500: Fix fstab after kitkat merge (2df4e29e05deaf6300131b3bfed5334a958950b5)

Change-Id: I6812311d208c3ab96387b87bbc1407c1522ecead