tests/qtest/migration: Make 'has_dirty_ring' generic

Keep accelerator knowledge limited within MigrationTestEnv,
expose a generic %has_dirty_ring value, only checking for
KVM when initializing it in migration_get_env().

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Message-ID: <20250128135429.8500-3-philmd@linaro.org>

tests/qtest/migration/framework.c

@@ -1108,7 +1108,7 @@ MigrationTestEnv *migration_get_env(void)
         return env;
     }
 
-    env->has_dirty_ring = kvm_dirty_ring_supported();
+    env->has_dirty_ring = env->has_kvm && kvm_dirty_ring_supported();
     env->has_uffd = ufd_version_check(&env->uffd_feature_thread_id);
     env->arch = qtest_get_arch();
     env->is_x86 = !strcmp(env->arch, "i386") || !strcmp(env->arch, "x86_64");

tests/qtest/migration/precopy-tests.c

@@ -1265,8 +1265,7 @@ void migration_test_add_precopy(MigrationTestEnv *env)
     if (g_test_slow()) {
         migration_test_add("/migration/auto_converge",
                            test_auto_converge);
-        if (g_str_equal(env->arch, "x86_64") &&
-            env->has_kvm && env->has_dirty_ring) {
+        if (g_str_equal(env->arch, "x86_64") && env->has_dirty_ring) {
             migration_test_add("/dirty_limit",
                                test_dirty_limit);
         }