arm64: dts: allwinner: h6: Add cooling map for GPU

Add a simple cooling map for the GPU.

This cooling map come from the vendor kernel 4.9 with a
2°C hysteresis added.

Signed-off-by: Clément Péron <peron.clem@gmail.com>
Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Link: https://lore.kernel.org/r/20220906153034.153321-3-peron.clem@gmail.com