dt-bindings: timer: mediatek: update bindings for MT7629 SoC

Update the binding for MT7629 SoC, which uses fallback compatible to
MT6765 SYST, so add more descriptions to distinguish it from the other
SoCs that use GPT.
Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

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

-Mediatek Timers
+MediaTek Timers
 ---------------
 
-Mediatek SoCs have two different timers on different platforms,
+MediaTek SoCs have two different timers on different platforms,
 - GPT (General Purpose Timer)
 - SYST (System Timer)
 
@@ -9,6 +9,7 @@ The proper timer will be selected automatically by driver.
 
 Required properties:
 - compatible should contain:
+	For those SoCs that use GPT
 	* "mediatek,mt2701-timer" for MT2701 compatible timers (GPT)
 	* "mediatek,mt6580-timer" for MT6580 compatible timers (GPT)
 	* "mediatek,mt6589-timer" for MT6589 compatible timers (GPT)
@@ -17,7 +18,11 @@ Required properties:
 	* "mediatek,mt8135-timer" for MT8135 compatible timers (GPT)
 	* "mediatek,mt8173-timer" for MT8173 compatible timers (GPT)
 	* "mediatek,mt6577-timer" for MT6577 and all above compatible timers (GPT)
-	* "mediatek,mt6765-timer" for MT6765 compatible timers (SYST)
+
+	For those SoCs that use SYST
+	* "mediatek,mt7629-timer" for MT7629 compatible timers (SYST)
+	* "mediatek,mt6765-timer" for MT6765 and all above compatible timers (SYST)
+
 - reg: Should contain location and length for timer register.
 - clocks: Should contain system clock.