mtd: s3c2410: Merge plat/regs-nand.h into s3c2410.c

plat/regs-nand.h is used only by S3C2410 nand driver. Since there
are no other users, merge this file into the driver code to remove
platform dependency. While at it also remove unused macros.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Acked-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>