mm: vm_event_item: explicit #include for THREAD_SIZE

This header uses THREAD_SIZE, which is provided by the thread_info.h
header but is not included in this header. Depending on the #include
ordering in other files, this can produce preprocessor errors.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Brian Norris <[e-mail]>
Reviewed-by: Lorenzo Stoakes <[e-mail]>
Cc: David Hildenbrand <[e-mail]>
Cc: Liam Howlett <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Mike Rapoport <[e-mail]>
Cc: Suren Baghdasaryan <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

include/linux/vm_event_item.h

···
 #ifndef VM_EVENT_ITEM_H_INCLUDED
 #define VM_EVENT_ITEM_H_INCLUDED
 
+#include <linux/thread_info.h>
+
 #ifdef CONFIG_ZONE_DMA
 #define DMA_ZONE(xx) xx##_DMA,
 #else