arm64: dts: rockchip: rk3588: add cpu frequency scaling support

Add required bits for CPU frequency scaling to the Rockchip 3588
devicetree. This is missing the 2.4 GHz operating point for the
big cpu clusters, since that does not work well on all SoCs.
Downstream has a driver for PVTM, which reduces the requested
frequencies based on (among other things) silicon quality.

Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>