i965: Fix gen6,gen7 when used with a non-HiZ capable DDX

Nothing works if HiZ is enabled and the DDX is incapable of HiZ (that is,
the DDX version is < 2.16).

The problem is that the refactoring that eliminated
intel_renderbuffer::stencil_rb broke the recovery path in
intel_verify_dri2_has_hiz().  Specifically, it broke line
intel_context.c:1445, which allocates the region for
DRI_BUFFER_DEPTH_STENCIL. That allocation was creating a separate stencil
miptree, despite the buffer being a packed depthstencil buffer. Havoc
ensued.

This patch introduces a bool flag that prevents allocation of that stencil
miptree.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=44103
Tested-by: Ian Romanick <idr@freedesktop.org>
Note: This is a candidate for the 8.0 branch.
Signed-off-by: Chad Versace <chad.versace@linux.intel.com>

src/mesa/drivers/dri/intel/intel_mipmap_tree.c

@@ -58,6 +58,11 @@ target_to_target(GLenum target)
    }
 }
 
+/**
+ * @param for_region Indicates that the caller is
+ *        intel_miptree_create_for_region(). If true, then do not create
+ *        \c stencil_mt.
+ */
 static struct intel_mipmap_tree *
 intel_miptree_create_internal(struct intel_context *intel,
 			      GLenum target,
@@ -66,7 +71,8 @@ intel_miptree_create_internal(struct intel_context *intel,
 			      GLuint last_level,
 			      GLuint width0,
 			      GLuint height0,
-			      GLuint depth0)
+			      GLuint depth0,
+			      bool for_region)
 {
    struct intel_mipmap_tree *mt = calloc(sizeof(*mt), 1);
    int compress_byte = 0;
@@ -106,7 +112,8 @@ intel_miptree_create_internal(struct intel_context *intel,
       mt->cpp = 2;
    }
 
-   if (_mesa_is_depthstencil_format(_mesa_get_format_base_format(format)) &&
+   if (!for_region &&
+       _mesa_is_depthstencil_format(_mesa_get_format_base_format(format)) &&
        (intel->must_use_separate_stencil ||
 	(intel->has_separate_stencil &&
 	 intel->vtbl.is_hiz_depth_format(intel, format)))) {
@@ -199,7 +206,8 @@ intel_miptree_create(struct intel_context *intel,
 
    mt = intel_miptree_create_internal(intel, target, format,
 				      first_level, last_level, width0,
-				      height0, depth0);
+				      height0, depth0,
+				      false);
    /*
     * pitch == 0 || height == 0  indicates the null texture
     */
@@ -234,7 +242,8 @@ intel_miptree_create_for_region(struct intel_context *intel,
 
    mt = intel_miptree_create_internal(intel, target, format,
 				      0, 0,
-				      region->width, region->height, 1);
+				      region->width, region->height, 1,
+				      true);
    if (!mt)
       return mt;