mtd: rawnand: Separate the ECC engine type and the ECC byte placement

The use of "syndrome" placement should not be encoded in the ECC
engine mode/type.

Create a "placement" field in NAND chip and change all occurrences of
the NAND_ECC_HW_SYNDROME enumeration to be just NAND_ECC_HW and
possibly a placement entry like NAND_ECC_PLACEMENT_INTERLEAVED.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://lore.kernel.org/linux-mtd/20200827085208.16276-10-miquel.raynal@bootlin.com