dt-bindings: usb: dwc2: Add reference to usb-drd.yaml

Add a reference to usb-drd.yaml, in order to:
- extend possible supported properties
- avoid duplicated definitions of standard properties
Remove definitions for dr_mode and usb-role-switch standard properties.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Link: https://lore.kernel.org/r/1634133425-25670-2-git-send-email-fabrice.gasnier@foss.st.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>