Add a typedef to for the fastop function prototype to make the code more
readable.

No functional change intended.
Signed-off-by: NSean Christopherson <sean.j.christopherson@intel.com>
Reviewed-by: NMiaohe Lin <linmiaohe@huawei.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>