ARM: dts: mvebu: armada-385-db-88f6820-amc: auto-detect nand ECC properites

This board has a Micron MT29F8G08ABACAWP chip which requires a ECC
strength of 8/512. Rather than hard coding any particular strength the
the nand controller auto-detect the ECC strength based on the ONFI data.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>