LoongArch: KVM: Set page with write attribute if dirty track disabled

LoongArch: KVM: Set page with write attribute if dirty track disabled

With secondary MMU page table, if there is a read page fault, the page's
write attribute will not set even if it is writable from master MMU page
table. This logic only works if dirty tracking is enabled, so page table
should be set with _PAGE_WRITE if dirty tracking is disabled.

It reduces extra page fault on secondary MMU page table if a VM finishes
migration, when the master MMU page table is ready and the secondary MMU
page is fresh.

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>