[ARM] pxa/cm-x300: use OBM configuration for NAND flash

CM-X300 can be assembled with different NAND flashes from different
manufacturers. Adding their configuration to the kernel is impractical,
therefore we will use the default NAND controller settings set up by the
bootloader.

Signed-off-by: Mike Rapoport <mike@compulab.co.il>
Signed-off-by: Eric Miao <eric.miao@marvell.com>