mtd: nand: raw: allow to disable unneeded ECC layouts

Each ECC layout consumes about 2984 bytes in the .data section. Allow
to disable the default ECC layouts if a driver is known to provide its
own ECC layout.

Signed-off-by: Stefan Agner <stefan.agner@toradex.com>
Reviewed-by: Lukasz Majewski <lukma@denx.de>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>