mtd: nand: s3c: Unify the register definition and naming

Merge struct s3c2410_nand and struct s3c2440_nand into one unified
struct s3c24x0_nand. While at it, fix up and rename the functions
to retrieve the NAND base address and fix up the s3c NAND driver to
reflect this change.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Lukasz Majewski <l.majewski@samsung.com>
Cc: Minkyu Kang <mk7.kang@samsung.com>
Cc: Scott Wood <scottwood@freescale.com>
Cc: Vladimir Zapolskiy <vz@mleia.com>