driver: ddr: Refine the ddr init driver on imx8m

Refine the ddr init driver to make it more reusable for different
DDR type(LPDDR4, DDR4 & DDR3L). So we can reduce some redundant
code.

Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Reviewed-by: Ye Li <ye.li@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/drivers/ddr/imx/imx8m/Kconfig b/drivers/ddr/imx/imx8m/Kconfig
index a83b0f4..5bf61eb 100644
--- a/drivers/ddr/imx/imx8m/Kconfig
+++ b/drivers/ddr/imx/imx8m/Kconfig
@@ -16,6 +16,12 @@
 	help
 	  Select the i.MX8M DDR4 driver support on i.MX8M SOC.
 
+config IMX8M_DDR3L
+	bool "imx8m ddr3l"
+	select IMX8M_DRAM
+	help
+	  Select the i.MX8M DDR3L driver support on i.MX8M SOC.
+
 config SAVED_DRAM_TIMING_BASE
 	hex "Define the base address for saved dram timing"
 	help