refactor(st-ddr): move basic tests in a dedicated file

These basic tests are generic and should be used independently of the
driver, depending on the plaftorm characteristics.

Change-Id: I38161b659ef2a23fd30a56e1c9b1bd98461a2fe4
Signed-off-by: Nicolas Le Bayon <nicolas.le.bayon@foss.st.com>
diff --git a/plat/st/stm32mp1/platform.mk b/plat/st/stm32mp1/platform.mk
index facc955..a24a5b0 100644
--- a/plat/st/stm32mp1/platform.mk
+++ b/plat/st/stm32mp1/platform.mk
@@ -297,7 +297,8 @@
 				plat/st/stm32mp1/stm32mp1_usb_dfu.c
 endif
 
-BL2_SOURCES		+=	drivers/st/ddr/stm32mp_ram.c				\
+BL2_SOURCES		+=	drivers/st/ddr/stm32mp_ddr_test.c			\
+				drivers/st/ddr/stm32mp_ram.c				\
 				drivers/st/ddr/stm32mp1_ddr.c				\
 				drivers/st/ddr/stm32mp1_ram.c