arm64: dts: rockchip: add passive GPU cooling on RK3588

As the GPU support on RK3588 has been merged upstream, along with OPP
values, add a corresponding cooling map for passive cooling using the GPU.

Signed-off-by: Alexey Charkov <alchark@gmail.com>
Link: https://lore.kernel.org/r/20240617-rk-dts-additions-v5-3-c1f5f3267f1e@gmail.com


Signed-off-by: Heiko Stuebner <heiko@sntech.de>