LoongArch: Disable module from accessing external data directly

The distance between vmlinux and the module is too far so that PC-REL
cannot be accessed directly, only GOT.

When compiling module with GCC, the option `-mdirect-extern-access` is
disabled by default. The Clang option `-fdirect-access-external-data` is
enabled by default, so it needs to be explicitly disabled.

Signed-off-by: WANG Rui <wangrui@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>