riscv: ae350: Fix OF_BOARD boot failure

Disable BINMAN_FDT for ae350 boards which don't actually use it.

Fixes: 836eac7c ("fdt: Make OF_BOARD a bool option")
Signed-off-by: Rick Chen <rick@andestech.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>