mtd: pxa3xx_nand: mtd scan id process could be defined by driver itself

Different NAND driver may require its unique detection. For pxa3xx_nand,
it use its self id database to get the necessary info.

Signed-off-by: Lei Wen <leiwen@marvell.com>
Signed-off-by: Haojian Zhuang <haojian.zhuang@marvell.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>