mainline inclusion
from mainline-4.20-rc1
commit: 196d9d8b
category: feature
feature: Reduce synchronous TLB invalidation on ARM64
bugzilla: NA
CVE: NA

--------------------------------------------------

In preparation for maintaining the mmu_gather code as its own entity,
move the implementation out of memory.c and into its own file.

Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NHanjun Guo <guohanjun@huawei.com>
Reviewed-by: NXuefeng Wang <wxf.wang@hisilicon.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>