configs: stm32f4xx: Remove CONFIG_SYS_RAM_FREQ_DIV

Since commit bfea69ad2793 ("stm32f7: sdram: correct sdram
configuration as per micron sdram"), CONFIG_SYS_RAM_FREQ_DIV
flag is no more used, remove it.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
3 files changed