dt-bindings: pwm: Update bindings for MT7629 SoC

This updates bindings for MT7629 pwm controller.
Signed-off-by: Sam Shih <sam.shih@mediatek.com>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/pwm/pwm-mediatek.txt

@@ -19,10 +19,15 @@ Required properties:
    - "pwm1-8": the eight per PWM clocks for mt2712
    - "pwm1-6": the six per PWM clocks for mt7622
    - "pwm1-5": the five per PWM clocks for mt7623
+   - "pwm1"  : the PWM1 clock for mt7629
  - pinctrl-names: Must contain a "default" entry.
  - pinctrl-0: One property must exist for each entry in pinctrl-names.
    See pinctrl/pinctrl-bindings.txt for details of the property values.
 
+Optional properties:
+- assigned-clocks: Reference to the PWM clock entries.
+- assigned-clock-parents: The phandle of the parent clock of PWM clock.
+
 Example:
 	pwm0: pwm@11006000 {
 		compatible = "mediatek,mt7623-pwm";