BACKPORT: FROMLIST: mm: move helper to check slub_debug_enabled

Move the helper to check slub_debug_enabled, so that we can confine the
use of #ifdef outside slub.c as well.

Link: https://lore.kernel.org/lkml/20210705103229.8505-2-yee.lee@mediatek.com/


Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Yee Lee <yee.lee@mediatek.com>
Suggested-by: Matthew Wilcox <willy@infradead.org>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Chinwen Chang <chinwen.chang@mediatek.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Kuan-Ying Lee <Kuan-Ying.Lee@mediatek.com>
Cc: Nicholas Tang <nicholas.tang@mediatek.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Bug: 193482732
Change-Id: If264d6e72224910e541e18e8d47ce5eb505f4abf
Signed-off-by: Yee Lee <yee.lee@mediatek.com>