imx8ulp_evk: Clear data at fdt_addr_r before booting kernel

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>