ARM: dts: berlin2q-marvell-dmp: add missing unit name to /memory node

This patch fixes the following DTC warning with W=1:

"Node /memory has a reg or ranges property, but no unit name"

Signed-off-by: Jisheng Zhang <jszhang@marvell.com>
Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>