[MTD] [NAND] S3C2410: Allow the machine code to get the BBT table from NAND

Added a flag to allow the machine code to tell the NAND
subsystem that it should try to pickup a BBT from the flash,
and also skip the NAND full scan at startup.

Signed-off-by: Michel Pollet <buserror@gmail.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>