Merge Pull Request from: @zhengzengkai 
 
Memory reliable feature is a memory tiering mechanism. It is based on
kernel mirror feature, which splits memory into two sperate regions,
mirrored(reliable) region and non-mirrored (non-reliable) region.

for kernel mirror feature:

    allocate kernel memory from mirrored region by default

    allocate user memory from non-mirrored region by default

non-mirrored region will be arranged into ZONE_MOVABLE.

for kernel reliable feature, it has additional features below:

    normal user tasks never alloc memory from mirrored region with userspace
    apis(malloc, mmap, etc.)

    special user tasks will allocate memory from mirrored region by default

    tmpfs/pagecache allocate memory from mirrored region by default

    upper limit of mirrored region allcated for user tasks, tmpfs and
    pagecache

Support Reliable fallback mechanism which allows special user tasks, tmpfs
and pagecache can fallback to alloc non-mirrored region, it's the default
setting.

In order to fulfil the goal

    ___GFP_RELIABILITY flag added for alloc memory from mirrored region.

    the high_zoneidx for special user tasks/tmpfs/pagecache is set to
    ZONE_NORMAL.

    normal user tasks could only alloc from ZONE_MOVABLE.

This patch is just the main framework, memory reliable support for special
user tasks, pagecache and tmpfs has own patches.

To enable this function, mirrored(reliable) memory is needed and
"kernelcore=reliable" should be added to kernel parameters. 
 
Link:https://gitee.com/openeuler/kernel/pulls/79 
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com> 
Signed-off-by: Xie XiuQi <xiexiuqi@huawei.com>