ARM: S3C: Add S3C_DEV_NAND Kconfig entry

Currently the S5PC100 does not define S3C_PA_NAND, leaving the NAND device
definitions in arch/arm/plat-s3c/dev-nand.c unbuildable. Add a KConfig
entry to select whether this is built.

As backwards compatibility, both the S3C24XX and S3C64XX define the new
configuration in their main Kconfig files until better support for basing
this selection on a per-machine basis can be sorted out.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>