ARM: dts: stm32: select otg mode for usbotg_hs on stm32746g_eval

Configure USB OTG HS in OTG (DRD) mode on STM32746G_eval.
The USB connector used will determine the role of USB OTG controller.

Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>