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

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We are preparing to add sparse vmemmap support to LoongArch. MIPS and
LoongArch need to call pgd_init()/pud_init()/pmd_init() when populating
page tables, so adjust their prototypes to make generic helpers can call
them.

NIOS2 declares pmd_init() but doesn't use, just remove it to avoid build
errors.
Reviewed-by: NJiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: NFeiyang Chen <chenfeiyang@loongson.cn>
Signed-off-by: NHuacai Chen <chenhuacai@loongson.cn>