dt-bindings: phy: phy-stm32-usbphyc: convert bindings to json-schema

Convert the STM32 USB PHY Controller (USBPHYC) bindings to DT schema format
using json-schema.

Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20201116171917.10447-1-amelie.delaunay@st.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>