mm, hugetlb_cgroup: align hugetlb cgroup limit to hugepage size

Memcg aligns memory.limit_in_bytes to PAGE_SIZE as part of the resource
counter since it makes no sense to allow a partial page to be charged.

As a result of the hugetlb cgroup using the resource counter, it is also
aligned to PAGE_SIZE but makes no sense unless aligned to the size of
the hugepage being limited.

Align hugetlb cgroup limit to hugepage size.

Signed-off-by: David Rientjes <rientjes@google.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>