efi: Fix UAF for arm64 when enable efi_fake_mem

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7F3NP


CVE: NA

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Efi fake mem support for arm64 is introduced for debug propose
only. However efi_memmap_init_late in arm_enable_runtime_services
will free this memory which will lead to UAF on efi.memmap.map.

In order to slove this, clear efi.memmap.flags to skip free.
Since efi map is never freed in arm64, this will not lead to
memroy leak.

Signed-off-by: Ma Wupeng <mawupeng1@huawei.com>