dt-bindings: timer: Add compatible for Mediatek MT8186

This commit adds dt-binding documentation of timer for Mediatek MT8186 SoC
Platform.
Signed-off-by: Allen-KH Cheng <Allen-KH.Cheng@mediatek.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220311130732.22706-2-allen-kh.cheng@mediatek.comSigned-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

Documentation/devicetree/bindings/timer/mediatek,mtk-timer.txt

@@ -23,6 +23,7 @@ Required properties:
 
 	For those SoCs that use SYST
 	* "mediatek,mt8183-timer" for MT8183 compatible timers (SYST)
+	* "mediatek,mt8186-timer" for MT8186 compatible timers (SYST)
 	* "mediatek,mt8192-timer" for MT8192 compatible timers (SYST)
 	* "mediatek,mt8195-timer" for MT8195 compatible timers (SYST)
 	* "mediatek,mt7629-timer" for MT7629 compatible timers (SYST)