KVM: MMU: audit: check whether have unsync sps after root sync

After root synced, all unsync sps are synced, this patch add a check to make
sure it's no unsync sps in VCPU's page table

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Avi Kivity <avi@redhat.com>