dt-bindings: mfd: Add STM32F7 RCC numeric constants into DT include file

This patch lists STM32F7's RCC numeric constants.
It will be used by clock and reset drivers, and DT bindings.

Signed-off-by: Gabriel Fernandez <gabriel.fernandez@st.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Alexandre TORGUE <alexandre.torgue@st.com>