As Linus suggested, kasan_mem_to_shadow()/kasan_shadow_to_mem() are not
performance-critical and too big to inline. This is simply wrong so just
define them out-of-line.

If they really need to be inlined in future, such as the objtool / SMAP
issue for X86, we should mark them __always_inline.
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>