linux-explicit-synchronization: Allow fences with opaque EGL buffers

Add opaque EGL buffers to the supported buffer types for use with the
explicit synchronization protocol. Opaque EGL buffers rely on the same
EGL implementation in both the compositor and clients, which makes it
straightforward to manage client expectations about fence support for
such buffers.

Also make it clearer that implementations are free to support other
buffer types beyond the required ones.

Signed-off-by: Alexandros Frantzis <alexandros.frantzis@collabora.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.com>

unstable/linux-explicit-synchronization/linux-explicit-synchronization-unstable-v1.xml

@@ -26,7 +26,7 @@
     DEALINGS IN THE SOFTWARE.
   </copyright>
 
-  <interface name="zwp_linux_explicit_synchronization_v1" version="1">
+  <interface name="zwp_linux_explicit_synchronization_v1" version="2">
     <description summary="protocol for providing explicit synchronization">
       This global is a factory interface, allowing clients to request
       explicit synchronization for buffers on a per-surface basis.
@@ -76,7 +76,7 @@
     </request>
   </interface>
 
-  <interface name="zwp_linux_surface_synchronization_v1" version="1">
+  <interface name="zwp_linux_surface_synchronization_v1" version="2">
     <description summary="per-surface explicit synchronization support">
       This object implements per-surface explicit synchronization.
 
@@ -101,8 +101,13 @@
       Each surface can be associated with only one object of this interface at
       any time.
 
-      Explicit synchronization is guaranteed to be supported only for buffers
-      created with any version of the wp_linux_dmabuf buffer factory.
+      In version 1 of this interface, explicit synchronization is only
+      guaranteed to be supported for buffers created with any version of the
+      wp_linux_dmabuf buffer factory. Version 2 additionally guarantees
+      explicit synchronization support for opaque EGL buffers, which is a type
+      of platform specific buffers described in the EGL_WL_bind_wayland_display
+      extension. Compositors are free to support explicit synchronization for
+      additional buffer types.
     </description>
 
     <request name="destroy" type="destructor">