i965/gen6 depth surface: calculate minimum array element being rendered

(a23cfb8 for gen6)

In layered rendering this will be 0. Otherwise it will be the
selected slice.

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/drivers/dri/i965/gen6_blorp.cpp

@@ -807,6 +807,8 @@ gen6_blorp_emit_depth_stencil_config(struct brw_context *brw,
                                    NULL,
                                    &tile_mask_x, &tile_mask_y);
 
+   const unsigned min_array_element = params->depth.layer;
+
    lod = params->depth.level - params->depth.mt->first_level;
 
    /* 3DSTATE_DEPTH_BUFFER */

src/mesa/drivers/dri/i965/gen6_depth_state.c

@@ -98,6 +98,8 @@ gen6_emit_depth_stencil_hiz(struct brw_context *brw,
       break;
    }
 
+   const unsigned min_array_element = irb ? irb->mt_layer : 0;
+
    lod = irb ? irb->mt_level - irb->mt->first_level : 0;
 
    BEGIN_BATCH(7);