LoongArch: KVM: Clear LLBCTL if secondary mmu mapping is changed

LLBCTL is a separated guest CSR register from host, host exception ERET
instruction will clear the host LLBCTL CSR register, and guest exception
will clear the guest LLBCTL CSR register.

VCPU0 atomic64_fetch_add_unless     VCPU1 atomic64_fetch_add_unless
     ll.d    %[p],  %[c]
     beq     %[p],  %[u], 1f

Here secondary mmu mapping is changed, host hpa page is replaced with a
new page. And VCPU1 will execute atomic instruction on the new page.

                                       ll.d    %[p],  %[c]
                                       beq     %[p],  %[u], 1f
                                       add.d   %[rc], %[p], %[a]
                                       sc.d    %[rc], %[c]
     add.d   %[rc], %[p], %[a]
     sc.d    %[rc], %[c]

LLBCTL is set on VCPU0 and it represents the memory is not modified by
other VCPUs, sc.d will modify the memory directly.

So clear WCLLB of the guest LLBCTL register when mapping is the changed.

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