mtd: nand: Add helpers to manage ECC engines and configurations

Add the logic in the NAND core to find the right ECC engine depending
on the NAND chip requirements and the user desires. Right now, the
choice may be made between (more will come):
* software Hamming
* software BCH
* on-die (SPI-NAND devices only)

Once the ECC engine has been found, the ECC engine must be
configured.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20201001102014.20100-2-miquel.raynal@bootlin.com