ARM: mach-bast: add NAND_SCAN_SILENT_NODEV to optional devices

Add the NAND_SCAN_SILENT_NODEV to the optional NAND devices that may not
be fitted to the board

Signed-off-by: Ben Dooks <ben@simtec.co.uk>
Signed-off-by: Simtec Linux Team <linux@simtec.co.uk>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>