kms-impl-simple: Add fake cursor planes if no real ones

Non-atomic drivers may support drmModeSetCursor() even if no cursor
plane is advertised. To deal with this, add a fake cursor plane for
every CRTC when using MetaKmsImplSimple. This will eventually be
translated to drmModeSetCursor() calls without any explicit cursor plane
usage.

Fixes: https://gitlab.gnome.org/GNOME/mutter/issues/1058

https://gitlab.gnome.org/GNOME/mutter/merge_requests/1079

src/backends/native/meta-kms-plane.h

@@ -27,12 +27,12 @@
 #include "backends/native/meta-kms-types.h"
 #include "backends/meta-monitor-transform.h"
 
-typedef enum _MetaKmsPlaneType
+enum _MetaKmsPlaneType
 {
   META_KMS_PLANE_TYPE_PRIMARY,
   META_KMS_PLANE_TYPE_CURSOR,
   META_KMS_PLANE_TYPE_OVERLAY,
-} MetaKmsPlaneType;
+};
 
 #define META_TYPE_KMS_PLANE meta_kms_plane_get_type ()
 G_DECLARE_FINAL_TYPE (MetaKmsPlane, meta_kms_plane,