gallium: add grid base to dispatch info

Vulkan device group support allows launching grids from
a grid base set of values. Add the interface for gallium

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Reviweed-by: Eric Anholt <eric@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8154>

src/gallium/include/pipe/p_state.h

@@ -873,6 +873,11 @@ struct pipe_grid_info
     */
    uint grid[3];
 
+   /**
+    * Base offsets to launch grids from
+    */
+   uint grid_base[3];
+
    /* Indirect compute parameters resource: If not NULL, block sizes are taken
     * from this buffer instead, which is laid out as follows:
     *