Some configs in loongson3_defconfig is invalid or needless,
use the following steps to update it:

make loongson3_defconfig
make savedefconfig
cp defconfig arch/mips/configs/loongson3_defconfig
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>