usb: dwc3: remove dwc3-qcom in favor of dwc3-of-simple

Now that we have a generic dwc3-of-simple.c, we can
use that instead of maintaining dwc3-qcom.c which is
extremely similar.

Cc: Ivan T. Ivanov <iivanov@mm-sol.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>