dt-bindings: thermal: r9a09g047-tsu: Document the TSU unit

dt-bindings: thermal: r9a09g047-tsu: Document the TSU unit

The Renesas RZ/G3E SoC includes a Thermal Sensor Unit (TSU) block designed
to measure the junction temperature. The device provides real-time
temperature measurements for thermal management, utilizing a single
dedicated channel (channel 1) for temperature sensing.

Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: John Madieu <john.madieu.xa@bp.renesas.com>
Link: https://lore.kernel.org/r/20250917170202.197929-2-john.madieu.xa@bp.renesas.com
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>