mtd: nand: mtk-ecc: also parse nand-ecc-engine if available

The recently added ECC engine support introduced a generic property
named nand-ecc-engine for ecc engine phandle. This patch adds support
for this new property.

Signed-off-by: Chuanhong Guo <gch981213@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20220424032527.673605-4-gch981213@gmail.com