arm64: kdump: Use page-level mapping for the high memory of crashkernel

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I545H8


CVE: NA

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If the crashkernel has both high memory above 4G and low memory under 4G,
kexec always loads the content such as Imge and dtb to the high memory
instead of the low memory. This means that only high memory requires write
protection based on page-level mapping. The allocation of high memory does
not depend on the DMA boundary. So we can reserve the high memory first
even if the crashkernel reservation is deferred.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>