arm64: dts: berlin4ct: Add L2 cache topology

This patch adds the L2 cache topology for berlin4ct which has 1MB L2
cache.

[Sebastian: rename cache node from "l2-cache" to "cache"]

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