FROMLIST: mm: create new include/linux/vm_event.h header file

Split off the definitions necessary to update event counters from vmstat.h
into a new vm_event.h file.

The rationale is to allow header files included from mm.h to update
counter events. vmstat.h can not be included from such header files,
because it refers to page_pgdat() which is only defined later down
in mm.h, and thus results in compile errors. vm_event.h does not refer
to page_pgdat() and thus does not result in such errors.

Signed-off-by: Michel Lespinasse <michel@lespinasse.org>
Link: https://lore.kernel.org/all/20220128131006.67712-31-michel@lespinasse.org/


Bug: 161210518
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Change-Id: Ie70dd435b3dcbad80a4a9bfc294b78a9107c1ac2