i965: Cite the 965 PRM for "the data cache is the sampler cache".

Presumably, this comment exists to justify the usage of
I915_GEM_DOMAIN_SAMPLER for this relocation.  At one point, this was
necessary to ensure that the right flushing was done to keep caches
coherent.  These days, the kernel just flushes everything, so I don't
think it matters.

Still, the comment is interesting, so leave it in place.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>

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

@@ -347,9 +347,9 @@ brw_create_constant_surface(struct brw_context *brw,
    surf[4] = 0;
    surf[5] = 0;
 
-   /* Emit relocation to surface contents.  Section 5.1.1 of the gen4
-    * bspec ("Data Cache") says that the data cache does not exist as
-    * a separate cache and is just the sampler cache.
+   /* Emit relocation to surface contents.  The 965 PRM, Volume 4, section
+    * 5.1.2 "Data Cache" says: "the data cache does not exist as a separate
+    * physical cache.  It is mapped in hardware to the sampler cache."
     */
    drm_intel_bo_emit_reloc(brw->batch.bo,
 			   *out_offset + 4,