ARM: dts: mvebu: align MTD partition nodes to dtschema

Update the node names for the SPI NOR and NAND partitions to conform to
the partition properties in the relevant dtschema.

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