feat(imx8m): add dram retention flow for imx8m family

Add the dram retention flow for i.MX8M SoC family.

Change-Id: Ifb8ba5b2f6f002133cf47c07fef73df29c51c890
Signed-off-by: Jacky Bai <ping.bai@nxp.com>
diff --git a/plat/imx/imx8m/imx8mp/platform.mk b/plat/imx/imx8m/imx8mp/platform.mk
index 73fbd87..ded31ca 100644
--- a/plat/imx/imx8m/imx8mp/platform.mk
+++ b/plat/imx/imx8m/imx8mp/platform.mk
@@ -15,6 +15,9 @@
 # Include GICv3 driver files
 include drivers/arm/gic/v3/gicv3.mk
 
+IMX_DRAM_SOURCES	:=	plat/imx/imx8m/ddr/dram.c		\
+				plat/imx/imx8m/ddr/dram_retention.c
+
 IMX_GIC_SOURCES		:=	${GICV3_SOURCES}			\
 				plat/common/plat_gicv3.c		\
 				plat/common/plat_psci_common.c		\
@@ -38,6 +41,7 @@
 				drivers/arm/tzc/tzc380.c			\
 				drivers/delay_timer/delay_timer.c		\
 				drivers/delay_timer/generic_delay_timer.c	\
+				${IMX_DRAM_SOURCES}				\
 				${IMX_GIC_SOURCES}				\
 				${XLAT_TABLES_LIB_SRCS}