arm64: dts: berlin4ct: support cpuidle-dt

This patch adds an idle-states node to describe the berlin4ct idle
states and also adds references to the idle-states node in all CPU
nodes. After this patch cpuidle is enabled.

Signed-off-by: Jisheng Zhang <jszhang@marvell.com>
Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>