mm: Disable watermark check if reliable fallback is disabled

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4SK3S


CVE: NA

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

If memory reliable watermark is far greater than zone's default watermark,
reliable memory allocation will trigger oom without wake up kswapd to
release pagecache.

With this patch, memory reliable watermark will be disabled if memory
fallback is disabled.

Signed-off-by: Ma Wupeng <mawupeng1@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>