dt-bindings: pwm: pwm-mediatek: Add documentation for MT8183 SoC

Add binding documentation for the MT8183 SoC.
Signed-off-by: Fabien Parent <fparent@baylibre.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

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

@@ -7,6 +7,7 @@ Required properties:
    - "mediatek,mt7623-pwm": found on mt7623 SoC.
    - "mediatek,mt7628-pwm": found on mt7628 SoC.
    - "mediatek,mt7629-pwm": found on mt7629 SoC.
+   - "mediatek,mt8183-pwm": found on mt8183 SoC.
    - "mediatek,mt8516-pwm": found on mt8516 SoC.
  - reg: physical base address and length of the controller's registers.
  - #pwm-cells: must be 2. See pwm.yaml in this directory for a description of