intel: Allocate s8z24 separate renderbuffers from AllocTextureImageBuffer().

Before, we were only allocating these from our TexImage, so if the
texture image was set up in any other way (non-accelerated
glGenerateMipmaps()), they'd be missing or wrong.

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

@@ -60,6 +60,11 @@ intel_alloc_texture_image_buffer(struct gl_context *ctx,
    struct gl_texture_object *texobj = image->TexObject;
    struct intel_texture_object *intel_texobj = intel_texture_object(texobj);
 
+   if (intel->must_use_separate_stencil
+       && image->TexFormat == MESA_FORMAT_S8_Z24) {
+      intel_tex_image_s8z24_create_renderbuffers(intel, intel_image);
+   }
+
    if (intel_texobj->mt &&
        intel_miptree_match_image(intel_texobj->mt, image)) {
       intel_miptree_reference(&intel_image->mt, intel_texobj->mt);

src/mesa/drivers/dri/intel/intel_tex.h

@@ -68,6 +68,9 @@ void intel_tex_map_images(struct intel_context *intel,
 
 void intel_tex_unmap_images(struct intel_context *intel,
                             struct intel_texture_object *intelObj);
+bool
+intel_tex_image_s8z24_create_renderbuffers(struct intel_context *intel,
+					   struct intel_texture_image *image);
 
 void intel_tex_image_s8z24_scatter(struct intel_context *intel,
 				   struct intel_texture_image *intel_image);

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

@@ -282,7 +282,7 @@ intel_tex_image_s8z24_gather(struct intel_context *intel,
    intel_tex_image_s8z24_scattergather(intel, intel_image, false);
 }
 
-static bool
+bool
 intel_tex_image_s8z24_create_renderbuffers(struct intel_context *intel,
 					   struct intel_texture_image *image)
 {