dt-bindings: usb: dwc2: add support for STM32MP15 SoCs USB OTG HS and FS

Add the specific compatible string for the DWC2 IP found in the STM32MP15
SoCs.
STM32MP15 SoCs uses sensing comparators to detect Vbus valid levels and
ID pin state. usb33d-supply described the regulator supplying Vbus and ID
sensing comparators.

Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Signed-off-by: Rob Herring <robh@kernel.org>