arm64: dts: rockchip: add reset property for dwc3 controllers on rk3399

After commit '06c47e62 usb: dwc3: of-simple: Add support to get resets
for the device' you can add the reset property to the dwc3 node, the reset
is required for the controller to work properly, otherwise bind / unbind
stress testing of the USB controller on rk3399 we'd often end up with lots
of failures that looked like this:

  phy phy-ff800000.phy.9: phy poweron failed --> -110
  dwc3 fe900000.dwc3: failed to initialize core
  dwc3: probe of fe900000.dwc3 failed with error -110

Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>