KVM: expose async pf through our standard mechanism

As Avi recently mentioned, the new standard mechanism for exposing features
is KVM_GET_SUPPORTED_CPUID, not spamming CAPs. For some reason async pf
missed that.

So expose async_pf here.

Signed-off-by: Glauber Costa <glommer@redhat.com>
CC: Gleb Natapov <gleb@redhat.com>
CC: Avi Kivity <avi@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/x86.c

@@ -2418,6 +2418,7 @@ static void do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
 		entry->eax = (1 << KVM_FEATURE_CLOCKSOURCE) |
 			     (1 << KVM_FEATURE_NOP_IO_DELAY) |
 			     (1 << KVM_FEATURE_CLOCKSOURCE2) |
+			     (1 << KVM_FEATURE_ASYNC_PF) |
 			     (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT);
 		entry->ebx = 0;
 		entry->ecx = 0;