LoongArch: Explicitly specify code model in Makefile

commit e67e0eb6a98b261caf45048f9eb95fd7609289c0 upstream.

LoongArch's toolchain may change the default code model from normal to
medium. This is unnecessary for kernel, and generates some relocations
which cannot be handled by the module loader. So explicitly specify the
code model to normal in Makefile (for Rust 'normal' is 'small').

Cc: stable@vger.kernel.org
Tested-by: Haiyong Sun <sunhaiyong@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>