LoongArch: mm: Fix huge page entry update for virtual machine

In virtual machine (guest mode), the tlbwr instruction can not write the
last entry of MTLB, so we need to make it non-present by invtlb and then
write it by tlbfill. This also simplify the whole logic.

Signed-off-by: Rui Wang <wangrui@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>