arm64: dts: rockchip: set rk3399 dynamic CPU power coefficients

Provide the dynamic power coefficient of the big and little CPU
clusters. These numbers are currently in use on the Samsung Chromebook
Plus ("Kevin").

The power allocator thermal governor doesn't know how to do anything if
it doesn't get power parameters from its cooling devices (in this case,
CPUfreq). So this effectively enables the power-allocator governor.

Signed-off-by: Brian Norris <briannorris@chromium.org>
[set the property in each core node]
Signed-off-by: Heiko Stuebner <heiko@sntech.de>