dt-bindings: usb: dwc2: Fix issues for stm32mp15x SoC

Correct the compatible list for stm32mp15x SoC.
Fix the name of the stm32mp15x dedicated supply to be aligned with
what the driver use.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>