Now that clk_stm32f7.c manages clocks for both STM32F4 and F7 SoCs
rename it to a more generic clk_stm32f.c

Fix also some checkpatch errors/warnings.
Signed-off-by: NPatrice Chotard <patrice.chotard@st.com>
Reviewed-by: NVikas Manocha <vikas.manocha@st.com>