memcg: rename MEM_CGROUP_CHARGE_TYPE_MAPPED as MEM_CGROUP_CHARGE_TYPE_ANON

Now, in memcg, 2 "MAPPED" enum/macro are found
 MEM_CGROUP_CHARGE_TYPE_MAPPED
 MEM_CGROUP_STAT_FILE_MAPPED

Thier names looks similar to each other but the former is used for
accounting anonymous memory. rename it as TYPE_ANON.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>