mtd: nand: fsmc: Add BCH4 SW ECC support for SPEAr600

mtd: nand: fsmc: Add BCH4 SW ECC support for SPEAr600

This patch adds support for 4-bit ECC BCH4 for the SPEAr600 SoC. This can
be used by boards equipped with a NAND chip that requires 4-bit ECC strength.
The SPEAr600 HW ECC only supports 1-bit ECC strength.

To enable SW BCH4, you need to specify this in your config header:

#define CONFIG_NAND_ECC_BCH
#define CONFIG_BCH

And use the command "nandecc bch4" to select this ECC scheme upon runtime.

Tested on SPEAr600 x600 board.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Scott Wood <scottwood@freescale.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>