i965: Apply depthstencil alignment workaround when doing fast clears.

Fast depth clears have the same depth/stencil alignment requirements
as other drawing operations.  Therefore, we need to call
brw_workaround_depthstencil_alignment() from both the clear and
drawing paths.

Without this fix, we get image corruption if the following conditions
hold: (a) the first ever drawing operation to a depth miplevel (or the
first drawing operation after having used the texture for sampling) is
a clear, (b) the depth miplevel has a size that is eligible for fast
depth clears, and (c) the depth miplevel has an offset within the
miptree that isn't 8x8 aligned.

Fixes piglit "depthstencil-render-miplevels" tests with size 273.

NOTE: This is a candidate for stable branches

Reviewed-by: Chad Versace <chad.versace@linux.intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>

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

@@ -40,6 +40,8 @@
 #include "intel_mipmap_tree.h"
 #include "intel_regions.h"
 
+#include "brw_context.h"
+
 #define FILE_DEBUG_FLAG DEBUG_BLIT
 
 static const char *buffer_names[] = {
@@ -219,7 +221,8 @@ brw_fast_clear_depth(struct gl_context *ctx)
 static void
 brw_clear(struct gl_context *ctx, GLbitfield mask)
 {
-   struct intel_context *intel = intel_context(ctx);
+   struct brw_context *brw = brw_context(ctx);
+   struct intel_context *intel = &brw->intel;
 
    if (!_mesa_check_conditional_render(ctx))
       return;
@@ -229,6 +232,7 @@ brw_clear(struct gl_context *ctx, GLbitfield mask)
    }
 
    intel_prepare_render(intel);
+   brw_workaround_depthstencil_alignment(brw);
 
    if (mask & BUFFER_BIT_DEPTH) {
       if (brw_fast_clear_depth(ctx)) {