mm: slub: make object_map_lock a raw_spinlock_t

The variable object_map is protected by object_map_lock. The lock is always
acquired in debug code and within already atomic context

Make object_map_lock a raw_spinlock_t.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>