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/ddr/imx/imx8m/Kconfig b/drivers/ddr/imx/imx8m/Kconfig
new file mode 100644
index 0000000..71f466f
--- /dev/null
+++ b/drivers/ddr/imx/imx8m/Kconfig
@@ -0,0 +1,22 @@
+config IMX8M_DRAM
+	bool "imx8m dram"
+
+config IMX8M_LPDDR4
+	bool "imx8m lpddr4"
+	select IMX8M_DRAM
+	help
+	  Select the i.MX8M LPDDR4 driver support on i.MX8M SOC.
+
+config IMX8M_DDR4
+	bool "imx8m ddr4"
+	select IMX8M_DRAM
+	help
+	  Select the i.MX8M DDR4 driver support on i.MX8M SOC.
+
+config SAVED_DRAM_TIMING_BASE
+	hex "Define the base address for saved dram timing"
+	help
+	  after DRAM is trained, need to save the dram related timming
+	  info into memory for low power use. OCRAM_S is used for this
+	  purpose on i.MX8MM.
+	default 0x180000