dt-bindings: mfd: Add STM32F4 RCC numeric constants into DT include file

Ths patch lists STM32F4's RCC numeric constants.
It will be used by clock and reset drivers, and DT bindings.

Signed-off-by: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Signed-off-by: Gabriel Fernandez <gabriel.fernandez@st.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>