qapi: Factor out compat_policy_input_ok()

The code to check policy for handling deprecated input is triplicated.
Factor it out into compat_policy_input_ok() before I mess with it in
the next commit.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20211028102520.747396-9-armbru@redhat.com>
[Policy code moved from qmp-dispatch.c to qapi-util.c to make visitors
link without qmp-dispatch.o]
diff --git a/qapi/qobject-input-visitor.c b/qapi/qobject-input-visitor.c
index c120dbd..f0b4c7c 100644
--- a/qapi/qobject-input-visitor.c
+++ b/qapi/qobject-input-visitor.c
@@ -14,6 +14,7 @@
 
 #include "qemu/osdep.h"
 #include <math.h>
+#include "qapi/compat-policy.h"
 #include "qapi/error.h"
 #include "qapi/qobject-input-visitor.h"
 #include "qapi/visitor-impl.h"
@@ -666,21 +667,9 @@
                                         unsigned special_features,
                                         Error **errp)
 {
-    if (!(special_features & 1u << QAPI_DEPRECATED)) {
-        return false;
-    }
-
-    switch (v->compat_policy.deprecated_input) {
-    case COMPAT_POLICY_INPUT_ACCEPT:
-        return false;
-    case COMPAT_POLICY_INPUT_REJECT:
-        error_setg(errp, "Deprecated parameter '%s' disabled by policy",
-                   name);
-        return true;
-    case COMPAT_POLICY_INPUT_CRASH:
-    default:
-        abort();
-    }
+    return !compat_policy_input_ok(special_features, &v->compat_policy,
+                                   ERROR_CLASS_GENERIC_ERROR,
+                                   "parameter", name, errp);
 }
 
 static void qobject_input_free(Visitor *v)