KVM: Add and use pr_unimpl for standard formatting of unimplemented features

All guest-invokable printks should be ratelimited to prevent malicious
guests from flooding logs.  This is a start.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Avi Kivity <avi@qumranet.com>
diff --git a/drivers/kvm/vmx.c b/drivers/kvm/vmx.c
index 3bf3650..ae54d9a 100644
--- a/drivers/kvm/vmx.c
+++ b/drivers/kvm/vmx.c
@@ -1920,7 +1920,7 @@
 		break;
 	}
 	kvm_run->exit_reason = 0;
-	printk(KERN_ERR "kvm: unhandled control register: op %d cr %d\n",
+	pr_unimpl(vcpu, "unhandled control register: op %d cr %d\n",
 	       (int)(exit_qualification >> 4) & 3, cr);
 	return 0;
 }