target-i386: add feature kvm_pv_unhalt

I don't know yet if want this feature on by default, so for now I'm
just adding support for "-cpu ...,+kvm_pv_unhalt".

Signed-off-by: Andrew Jones <drjones@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

target-i386/cpu.c

@@ -235,7 +235,7 @@ static const char *ext4_feature_name[] = {
 
 static const char *kvm_feature_name[] = {
     "kvmclock", "kvm_nopiodelay", "kvm_mmu", "kvmclock",
-    "kvm_asyncpf", "kvm_steal_time", "kvm_pv_eoi", NULL,
+    "kvm_asyncpf", "kvm_steal_time", "kvm_pv_eoi", "kvm_pv_unhalt",
     NULL, NULL, NULL, NULL,
     NULL, NULL, NULL, NULL,
     NULL, NULL, NULL, NULL,