usb: dwc2: add support for the DWC2 controller on Meson8 SoCs

USB support in the Meson8 SoCs is provided by a DWC2 controller which
works with the same settings as Meson8b and GXBB. Using the generic
"snps,dwc2" binding results in an endless stream of "Overcurrent change
detected" messages.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>