imx: imx8qm: update fdt_file according to m4 state

Update fdt_file according to m4 parts state

Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/board/freescale/imx8qm_mek/imx8qm_mek.c b/board/freescale/imx8qm_mek/imx8qm_mek.c
index c9b9b25..c0cae35 100644
--- a/board/freescale/imx8qm_mek/imx8qm_mek.c
+++ b/board/freescale/imx8qm_mek/imx8qm_mek.c
@@ -123,10 +123,23 @@
 
 int board_late_init(void)
 {
+	char *fdt_file;
+	bool m4_booted;
+
 #ifdef CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG
 	env_set("board_name", "MEK");
 	env_set("board_rev", "iMX8QM");
 #endif
 
+	fdt_file = env_get("fdt_file");
+	m4_booted = m4_parts_booted();
+
+	if (fdt_file && !strcmp(fdt_file, "undefined")) {
+		if (m4_booted)
+			env_set("fdt_file", "imx8qm-mek-rpmsg.dtb");
+		else
+			env_set("fdt_file", "imx8qm-mek.dtb");
+	}
+
 	return 0;
 }