usb: dwc3: qcom: Add support for MSM8998

Add a MSM8998 specific DT compatible so that we can properly bind to the
device and enable the USB controller.

Reviewed-by: Andy Gross <andy.gross@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>