mtd: nand: davinci: set ECC algorithm explicitly for HW based ECC

If ECC strength is 4bits/512bytes the algorithm of the ECC engine is
BCH, otherwise (1bit/512bytes) Hamming is used.

Signed-off-by: Alexander Couzens <lynxis@fe80.eu>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>