imx8ulp_evk: Clear data at fdt_addr_r before booting kernel

When using dual boot mode, the DDR won't be reset when APD power off
or reboot. It has possibility that obsolete fdt data existing on
fdt_addr_r address. Then even nothing in EFI partitions, the distro boot
still continue to parse fdt and get uboot crashed.

Clear the data at fdt_addr_r, so the fdt header check in above case
will not pass.

Signed-off-by: Ye Li <ye.li@nxp.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
diff --git a/board/freescale/imx8ulp_evk/imx8ulp_evk.c b/board/freescale/imx8ulp_evk/imx8ulp_evk.c
index b58f143..dd04d59 100644
--- a/board/freescale/imx8ulp_evk/imx8ulp_evk.c
+++ b/board/freescale/imx8ulp_evk/imx8ulp_evk.c
@@ -121,8 +121,16 @@
 
 int board_late_init(void)
 {
+	ulong addr;
+
 #if CONFIG_IS_ENABLED(ENV_IS_IN_MMC)
 	board_late_mmc_env_init();
 #endif
+
+	/* clear fdtaddr to avoid obsolete data */
+	addr = env_get_hex("fdt_addr_r", 0);
+	if (addr)
+		memset((void *)addr, 0, 0x400);
+
 	return 0;
 }