i965: Add comments to the new brw_state_state structure's fields.

These are largely based on the similar fields in brw->wm.

v2: Add a better comment than "Scratch buffer".

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Paul Berry <stereotype441@gmail.com>

src/mesa/drivers/dri/i965/brw_context.h

@@ -835,15 +835,25 @@ struct brw_query_object {
  */
 struct brw_stage_state
 {
+   /**
+    * Optional scratch buffer used to store spilled register values and
+    * variably-indexed GRF arrays.
+    */
    drm_intel_bo *scratch_bo;
+
+   /** Pull constant buffer */
    drm_intel_bo *const_bo;
+
    /** Offset in the program cache to the program */
    uint32_t prog_offset;
+
+   /** Offset in the batchbuffer to Gen4-5 pipelined state (VS/WM/GS_STATE). */
    uint32_t state_offset;
 
    uint32_t push_const_offset; /* Offset in the batchbuffer */
    int push_const_size; /* in 256-bit register increments */
 
+   /* Binding table: pointers to SURFACE_STATE entries. */
    uint32_t bind_bo_offset;
    uint32_t surf_offset[BRW_MAX_VEC4_SURFACES];