dts: arm: nxp: move power-states to soc dts files

CPU idle states are not board specific. This patch moves NXP idle states
to the core SoC dts files. Board can always tweak some state parameters
(if needed), but the definition belongs to core SoC dts files, same as
e.g.  peripherals.

Signed-off-by: Gerard Marull-Paretas <gerard@teslabs.com>