arm64: dts: renesas: r8a779f0: Add CPUIdle support

Support CPUIdle for ARM Cortex-A55 on R-Car S4-8.

Signed-off-by: Tho Vu <tho.vu.wh@renesas.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Tested-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/5310792ce4c06515a5373ff44ceb9b925f007489.1654701480.git.geert+renesas@glider.be