dt-bindings: phy: cdns,salvo: add property cdns,usb2-disconnect-threshold-microvolt

Add cdns,usb2-disconnect-threshold-microvolt property to address fake USB
disconnection issue during enumeration or suspend state for difference
platform.

Reviewed-by: Krzysztof Kozlowski <[e-mail]>
Signed-off-by: Frank Li <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

Documentation/devicetree/bindings/phy/cdns,salvo-phy.yaml

···
   "#phy-cells":
     const: 0
 
+  cdns,usb2-disconnect-threshold-microvolt:
+    description: The microvolt threshold value utilized for detecting
+      USB disconnection event.
+    enum: [575, 610, 645]
+    default: 575
+
 required:
   - compatible
   - reg