[MTD] NAND: s3c24xx updates

Fix error in timing generation, Tacls is only in the range 0..3

Add proper support for the s3c2440 NAND controller, which has now
been tested on several s3c2440 implementations.

Signed-off-by: Ben Dooks <ben@simtec.co.uk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>