mm: Update reliable flag in memory allocaion for reliable task only in task context

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


CVE: NA

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Since interrupt may occupy reliable task's context and its current->flags
will have PF_RELIABLE and this will lead to redirect it's memory allocation
to mirrored region.

In order to solve this problem, update reliable task's gfp flag can only
happen in normal task context by checking in_task().

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