LoongArch inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5OHOB

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Add sparse memory vmemmap support for LoongArch. SPARSEMEM_VMEMMAP
uses a virtually mapped memmap to optimise pfn_to_page and page_to_pfn
operations. This is the most efficient option when sufficient kernel
resources are available.
Signed-off-by: NMin Zhou <zhoumin@loongson.cn>
Signed-off-by: NFeiyang Chen <chenfeiyang@loongson.cn>
Signed-off-by: NHuacai Chen <chenhuacai@loongson.cn>