mtd: nand: raw: Add support for DT property nand-ecc-algo=bch

According to Linux kernel DT schema nand-controller.yaml, using DT property
nand-ecc-algo=bch is the correct way for specifying BCH as ECC algorithm.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>