stm32f7: sdram: move sdram driver code to ram drivers area

Signed-off-by: Vikas Manocha <vikas.manocha@st.com>
cc: Christophe KERELLO <christophe.kerello@st.com>
diff --git a/drivers/ram/Makefile b/drivers/ram/Makefile
index 0e10249..ecb036d 100644
--- a/drivers/ram/Makefile
+++ b/drivers/ram/Makefile
@@ -6,3 +6,4 @@
 #
 obj-$(CONFIG_RAM) += ram-uclass.o
 obj-$(CONFIG_SANDBOX) += sandbox_ram.o
+obj-$(CONFIG_STM32_SDRAM) += stm32_sdram.o