dts: bindings: usb: Introduce STM32N6 OTG HS compatible

Add STM32N6 USB OTG HS compatible 'st,stm32n6-otghs'
that doesn't require pinctrl-0 and pinctrl-names.

Signed-off-by: IBEN EL HADJ MESSAOUD Marwa <marwa.ibenelhadjmessaoud-ext@st.com>