dt-bindings: thermal: convert Mediatek Thermal to the json-schema

This helps validating DTS files. Introduced changes:
1. Improved title
2. Simplified description (dropped "This describes the device tree...")
3. Dropped undocumented "reset-names" from example

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20231117052214.24554-1-zajec5@gmail.com