ram: stm32: migrate fmc defines in driver file

Migrate all FMC defines from arch/arm/include/asm/arch-stm32f7/fmc.h
to drivers/ram/stm32_sdram.c

This will avoid to add an additionnal arch-stm32xx/fmc.h file when
a new stm32 family soc will be introduced.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Vikas Manocha <vikas.manocha@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>