arm64: dts: meson: g12: Add minimal thermal zone

Add minimal thermal zone for two temperature sensor
One is located close to the DDR and the other one is
located close to the PLLs (between the CPU and GPU)

Acked-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Amit Kucheria <amit.kucheria@linaro.org>
Tested-by: Christian Hewitt <christianshewitt@gmail.com>
Tested-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Guillaume La Roque <glaroque@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>