dt-bindings: pwm: fix microchip corePWM's pwm-cells

[ Upstream commit a62d196 ]

corePWM is capable of inverted operation but the binding requires
\#pwm-cells of 2. Expand the binding to support setting the polarity.

Fixes: df77f77 ("dt-bindings: pwm: add microchip corepwm binding")
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Documentation/devicetree/bindings/pwm/microchip,corepwm.yaml

@@ -30,7 +30,9 @@ properties:
     maxItems: 1
 
   "#pwm-cells":
-    const: 2
+    enum: [2, 3]
+    description:
+      The only flag supported by the controller is PWM_POLARITY_INVERTED.
 
   microchip,sync-update-mask:
     description: |