dt-bindings: usb: add missed compatible string for arm64 layerscape

Add missed compatible string for arm64 layerscape platform. Allow these
fallback to fsl,ls1028a-dwc3.

Remove fallback snps,dwc3 because layerscape dwc3 is not full compatible
with common snps,dwc3 device, a special value gsburstcfg0 need be set when
dma coherence enabled.

Allow iommus property.

Change ref to snps,dwc3-common.yaml to use dwc3 flatten library.

Reviewed-by: Rob Herring (Arm) <[e-mail]>
Signed-off-by: Frank Li <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/devicetree/bindings/usb/fsl,ls1028a.yaml

···
 maintainers:
   - Frank Li <[e-mail]>
 
-select:
-  properties:
-    compatible:
-      contains:
-        enum:
-          - fsl,ls1028a-dwc3
-  required:
-    - compatible
-
 properties:
   compatible:
-    items:
-      - enum:
-          - fsl,ls1028a-dwc3
-      - const: snps,dwc3
+    oneOf:
+      - items:
+          - enum:
+              - fsl,ls1012a-dwc3
+              - fsl,ls1043a-dwc3
+              - fsl,ls1046a-dwc3
+              - fsl,ls1088a-dwc3
+              - fsl,ls208xa-dwc3
+              - fsl,lx2160a-dwc3
+          - const: fsl,ls1028a-dwc3
+      - const: fsl,ls1028a-dwc3
 
   reg:
     maxItems: 1
 
   interrupts:
     maxItems: 1
+
+  iommus:
+    maxItems: 1
+
+  dma-coherent: true
 
 unevaluatedProperties: false
 
···
   - interrupts
 
 allOf:
-  - $ref: snps,dwc3.yaml#
+  - $ref: snps,dwc3-common.yaml#
 
 examples:
   - |
     #include <dt-bindings/interrupt-controller/arm-gic.h>
 
     usb@fe800000 {
-        compatible = "fsl,ls1028a-dwc3", "snps,dwc3";
+        compatible = "fsl,ls1028a-dwc3";
         reg = <0xfe800000 0x100000>;
         interrupts = <GIC_SPI 105 IRQ_TYPE_LEVEL_HIGH>;
     };