dt-bindings: thermal: rzg2l-thermal: Document RZ/G2UL bindings

dt-bindings: thermal: rzg2l-thermal: Document RZ/G2UL bindings

Document RZ/G2UL TSU bindings. The TSU block on RZ/G2UL is identical to one
found on RZ/G2L SoC. No driver changes are required as generic compatible
string "renesas,rzg2l-tsu" will be used as a fallback.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220501081930.23743-1-biju.das.jz@bp.renesas.com
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>