ARM: dts: meson8b: add the thermal-zones with cooling configuration

The vendor kernel uses the following thermal-zone settings:
<= 70°C:
- CPU frequency limited to 1.488GHz
- GPU limited to 511MHz and 2 cores (pixel processors)

<= 80°C:
- CPU frequency limited to 1.2GHz
- GPU limited to 435MHz and 2 cores (pixel processors)

<= 90°C:
- CPU frequency limited to 0.804GHz
- GPU limited to 328MHz and 1 core (pixel processor)

Add simplified thermal configuration which is taken from the
GXBB/GXL/GXM SoC family (which uses the same manufacturing process and
has the same maximum junction temperature of 125°C). With this the
thermal framework will try to keep the SoC temperature at or below 80°C
which is identical to the vendor kernel (with the exception of one CPU
frequency step from 1.488GHz to 1.536GHz).

The number of GPU cores are not taken into account as this is not
supported.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Link: https://lore.kernel.org/r/20201221181306.904272-5-martin.blumenstingl@googlemail.com