arm64: dts: marvell: add NAND support on the 8040-DB board

Add NAND support on the Armada-8040-DB by adding the same tree as for
the Armada-7040-DB by using the same compatible string
"marvell,armada-8k-nand".

Do not enable the NAND node as enabling it (and changing manually the
proper DPR-76 switch) would disable MDIO from CP1 (and thus disable CPS
Ethernet PHY).

Signed-off-by: Miquel Raynal <miquel.raynal@free-electrons.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>