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

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) <robh@kernel.org>
Signed-off-by: Frank Li <Frank.Li@nxp.com>
Link: https://lore.kernel.org/r/20250929-ls_dma_coherence-v5-1-2ebee578eb7e@nxp.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>