include: zephyr: dt-bindings: Add STM32C0 USB clock selection support

- Defined CCIPR2_REG offset.
- Added USB_SEL(val) macro to support USB clock selection using CCIPR2_REG.

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