arm64: dts: renesas: r8a7796: Add OPPs table for cpu devices

Define OOP tables for all CPUs.
This allows CPUFreq to function.

Based in part on work by Hien Dang.

Signed-off-by: Dien Pham <dien.pham.ry@rvc.renesas.com>
Signed-off-by: Takeshi Kihara <takeshi.kihara.df@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>