Move machine specific code to board at s3c64xx (v2)

Move machine specific code to smdk6400.
Some board use OneNAND instead of NAND.

Some register MP0_CS_CFG[5:0] are controled by both h/w and s/w.
So it's better to use macro instead of hard-coded value.

Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>