mtd: s3c nand: parsing command-line partitions prior to set->partitions

Current driver prevents command-line partitions from being parsed when built-in
partitions are defined in s3c2410_nand_set object, but it is not desirable in some
cases. This patch tries to parse commad-line partitions prior to the built-in.

Signed-off-by: Conke Hu <conke@maxwit.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>