usb: dwc3: add layerscape support

usb: dwc3: add layerscape support

Add support for the proper dwc3 device tree binding support as specified
in the offical device tree spec.

Initially, add support for the LS1028A support. Other SoCs should be
easy to add by just adding the corresponding compatible string.
Unfortunately, the device trees of all other layerscape SoCs are not
converted and uses a wrong compatible string only known in u-boot.

To maintain backwards compatibility with current u-boot device trees,
add the generic "fsl,layerscape-dwc3" compatible string.

OTG mode is not supported yet. The dr_mode in the devicetree will either
have to be set to peripheral or host.

Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>