mtd: nand: Rename a core structure

Prepare the migration to a generic ECC engine by renaming the
nand_ecc_req structure into nand_ecc_props. This structure will be the
base of a wider 'nand_ecc' structure.

In nand_device, these properties are still named "eccreq" even if
"eccprops" might be more descriptive. This is just a transition step,
this field is being replaced very soon by a much wider structure. The
impact of renaming this field would be huge compared to its interest.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://lore.kernel.org/linux-mtd/20200529002517.3546-14-miquel.raynal@bootlin.com