drivers: ddr: introduce DDR driver for i.MX8M

Introduce DDR driver for i.MX8M. The driver will be used by SPL to
initialze DDR PHY and DDR Controller.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/drivers/Makefile b/drivers/Makefile
index 752caea..c3c0615 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -34,6 +34,7 @@
 obj-$(CONFIG_ARMADA_38X) += ddr/marvell/a38x/
 obj-$(CONFIG_ARMADA_XP) += ddr/marvell/axp/
 obj-$(CONFIG_ALTERA_SDRAM) += ddr/altera/
+obj-$(CONFIG_ARCH_IMX8M) += ddr/imx/imx8m/
 obj-$(CONFIG_SPL_POWER_SUPPORT) += power/ power/pmic/
 obj-$(CONFIG_SPL_POWER_SUPPORT) += power/regulator/
 obj-$(CONFIG_SPL_POWER_DOMAIN) += power/domain/