mvebu: revert remove of mvsw61xx device tree nodes

The marvell,88e6352 and marvell,88e6172 compatible strings are used in
target/linux/generic/files/drivers/net/phy/mvsw61xx.c. No idea why grep
missed them when I searched for them.

Thanks to Syrone Wong for noticing and reporting my mistake.

Signed-off-by: Mathias Kresin <dev@kresin.me>