dri2: Add __DRI_BUFFER_COUNT token

Remove definition from egl_dri2.
Defining this is egl_dri2.h breaks as soon as
a new dri2 buffer token is added like with commit
4501a5d6.

include/GL/internal/dri_interface.h

@@ -694,6 +694,9 @@ struct __DRIswrastExtensionRec {
 #define __DRI_BUFFER_DEPTH_STENCIL	9  /**< Only available with DRI2 1.1 */
 #define __DRI_BUFFER_HIZ		10
 
+/* Inofficial and for internal use. Increase when adding a new buffer token. */
+#define __DRI_BUFFER_COUNT		11
+
 struct __DRIbufferRec {
     unsigned int attachment;
     unsigned int name;

src/egl/drivers/dri2/egl_dri2.h

@@ -123,8 +123,6 @@ enum wayland_buffer_type {
    WL_BUFFER_THIRD,
    WL_BUFFER_COUNT
 };
-
-#define __DRI_BUFFER_COUNT 10
 #endif
 
 enum dri2_surface_type {