According to Documentation/devicetree/bindings/arm/cpus.yaml, the
"enable-method" property should be a property of the individual CPU
nodes, and not of the parent "cpus" container node.
However, on R-Car Gen2 and RZ/G1 SoCs, the property is tied to the
"cpus" node instead.

Secondary CPU bringup and CPU hot (un)plug work regardless, as
arm_dt_init_cpu_maps() falls back to looking in the "cpus" node.

The cpuidle code does not have such a fallback, so it does not detect
the enable-method.  Note that cpuidle does not support the
"renesas,apmu" enable-method yet, so for now this does not make any
difference.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/35fcfedf9de9269185c48ca5a6dfcba7cdd3484b.1621427319.git.geert+renesas@glider.be