usb: dwc2: add "u-boot,force-vbus-detection" for stm32

On some board, the ID pin is not connected so the B session must be
overridden with "u-boot,force_b_session_valid" but the VBus sensing
must continue to be handle.

To managed it, this patch adds a new DT field
"u-boot,force-vbus-detection" to use with "u-boot,force_b_session_valid"

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
diff --git a/include/usb/dwc2_udc.h b/include/usb/dwc2_udc.h
index a2af381..aa37e95 100644
--- a/include/usb/dwc2_udc.h
+++ b/include/usb/dwc2_udc.h
@@ -28,6 +28,7 @@
 	unsigned int	tx_fifo_sz_array[DWC2_MAX_HW_ENDPOINTS];
 	unsigned char   tx_fifo_sz_nb;
 	bool		force_b_session_valid;
+	bool		force_vbus_detection;
 	bool		activate_stm_id_vb_detection;
 };