imx: imx8mn_evk: Enable dynamic settings to mmcdev and mmcroot

Enable dynamic settings to mmcdev and mmcroot for i.MX8MN-EVK

Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/board/freescale/imx8mn_evk/imx8mn_evk.c b/board/freescale/imx8mn_evk/imx8mn_evk.c
index 1b9dc51..c62d7a4 100644
--- a/board/freescale/imx8mn_evk/imx8mn_evk.c
+++ b/board/freescale/imx8mn_evk/imx8mn_evk.c
@@ -3,6 +3,7 @@
  * Copyright 2019 NXP
  */
 
+#include <asm/arch/sys_proto.h>
 #include <asm/io.h>
 #include <env.h>
 #include <init.h>
@@ -30,6 +31,10 @@
 
 int board_late_init(void)
 {
+#if CONFIG_IS_ENABLED(ENV_IS_IN_MMC)
+	board_late_mmc_env_init();
+#endif
+
 #ifdef CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG
 	env_set("board_name", "DDR4 EVK");
 	env_set("board_rev", "iMX8MN");