linux-phytec-fsl

arm64: dts: ls208xa: add cpu idle support

ls208xa supports another cpu idle state which is pw20 which saves
more power when cpu is idle.
It was implemented through psci firmware.

Signed-off-by: Tang Yuantian <andy.tang@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>