forked from Mirrors/opensbi

U-Boot readme for fu540 platform suggest that fdt_addr_r should be used as DT address after DT is copied via tftpboot. Update the OpenSBI docs to reflect that. Remove other stale informations as well. Signed-off-by: Atish Patra <atish.patra@wdc.com> Reviewed-by: Anup Patel <anup.patel@wdc.com>