arm64: dts: rockchip: reduce thermal limits on rk3399-pinephone-pro

While this device uses the rk3399 it is also enclosed in a tight package
and cooled through the screen and back case. The default rk3399 thermal
limits can result in a burnt screen.

These lower limits have resulted in the existing burn not expanding and
will hopefully result in future devices not experiencing the issue.

Signed-off-by: Jarrah Gosbell <kernel@undef.tools>
Link: https://lore.kernel.org/r/20221207113212.8216-1-kernel@undef.tools
Signed-off-by: Heiko Stuebner <heiko@sntech.de>