mm: gmem: Save vm_flags to gmf during mmap

euleros inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7WLVX



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During mmap_region, vm_flags is not save in gmf which lead to prot
in gmf is always VM_NONE.

To fix this, update prot to gmf during init.

Fixes: 848492f2 ("mm: gmem: Introduce vm_object for gmem")
Signed-off-by: Ma Wupeng <mawupeng1@huawei.com>