migration: Move migrate_colo_enabled() to options.c

Once that we are there, we rename the function to migrate_colo() to be
consistent with all other capabilities.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
diff --git a/migration/options.c b/migration/options.c
index 88a9a45..bd33c5d 100644
--- a/migration/options.c
+++ b/migration/options.c
@@ -33,6 +33,12 @@
     return s->capabilities[MIGRATION_CAPABILITY_BACKGROUND_SNAPSHOT];
 }
 
+bool migrate_colo(void)
+{
+    MigrationState *s = migrate_get_current();
+    return s->capabilities[MIGRATION_CAPABILITY_X_COLO];
+}
+
 bool migrate_dirty_bitmaps(void)
 {
     MigrationState *s;