gbm: Add new gbm_bo_import entry point

This generalizes and replaces gbm_bo_create_for_egl_image.  gbm_bo_import
will create a gbm_bo from either an EGLImage or a struct wl_buffer.
diff --git a/src/mesa/drivers/dri/intel/intel_screen.c b/src/mesa/drivers/dri/intel/intel_screen.c
index bcd85e9..6daeb05 100644
--- a/src/mesa/drivers/dri/intel/intel_screen.c
+++ b/src/mesa/drivers/dri/intel/intel_screen.c
@@ -357,7 +357,13 @@
    case __DRI_IMAGE_ATTRIB_FORMAT:
       *value = image->dri_format;
       return true;
-   default:
+   case __DRI_IMAGE_ATTRIB_WIDTH:
+      *value = image->region->width;
+      return true;
+   case __DRI_IMAGE_ATTRIB_HEIGHT:
+      *value = image->region->height;
+      return true;
+  default:
       return false;
    }
 }