dt-bindings: phy: imx8mq-usb: add alternate reference clock

Beside default 24MHz clock input, there is an optional additional 100Mhz
clock input 'alt' for USB PHY reference clock.

Reviewed-by: Frank Li <Frank.Li@nxp.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
Link: https://patch.msgid.link/20251118071947.2504789-1-xu.yang_2@nxp.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

Author: Xu Yang

Documentation/devicetree/bindings/phy/fsl,imx8mq-usb-phy.yaml

@@ -27,11 +27,16 @@ properties:
     const: 0
 
   clocks:
-    maxItems: 1
+    minItems: 1
+    items:
+      - description: PHY configuration clock
+      - description: Alternate PHY reference clock
 
   clock-names:
+    minItems: 1
     items:
       - const: phy
+      - const: alt
 
   power-domains:
     maxItems: 1