LoongArch: KVM: Discard dirty page tracking on readonly memslot

LoongArch: KVM: Discard dirty page tracking on readonly memslot

For readonly memslot such as UEFI BIOS or UEFI var space, guest cannot
write this memory space directly. So it is not necessary to track dirty
pages for readonly memslot. Here we make such optimization in function
kvm_arch_commit_memory_region().

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