gbm: track buffer format through DRI drivers

GBM needs the buffer format in order to communicate with DRM and clients
for things like scanout.

So track the DRI format requested in the various back ends and use it to
return the DRI format back to GBM when requested.  GBM will then map
this into the GBM surface type (which is in turn based on the DRM fb
format list).

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

include/GL/internal/dri_interface.h

@@ -894,7 +894,7 @@ struct __DRIdri2ExtensionRec {
  * extensions.
  */
 #define __DRI_IMAGE "DRI_IMAGE"
-#define __DRI_IMAGE_VERSION 2
+#define __DRI_IMAGE_VERSION 3
 
 /**
  * These formats correspond to the similarly named MESA_FORMAT_*
@@ -918,6 +918,7 @@ struct __DRIdri2ExtensionRec {
 #define __DRI_IMAGE_ATTRIB_STRIDE	0x2000
 #define __DRI_IMAGE_ATTRIB_HANDLE	0x2001
 #define __DRI_IMAGE_ATTRIB_NAME		0x2002
+#define __DRI_IMAGE_ATTRIB_FORMAT	0x2003 /* available in versions 3+ */
 
 typedef struct __DRIimageRec          __DRIimage;
 typedef struct __DRIimageExtensionRec __DRIimageExtension;