anv/image: Fix interpretation of 'disjoint'

The calculation of the subsurfaces' memory requirements assumed that the
image was disjoint if the image was created with
VK_IMAGE_CREATE_DISJOINT_BIT. But the Vulkan spec also requires that the
VkFormat be multi-planar.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8097>

src/intel/vulkan/anv_private.h

@@ -3759,8 +3759,9 @@ struct anv_image {
    VkDeviceSize size;
    uint32_t alignment;
 
-   /* Whether the image is made of several underlying buffer objects rather a
-    * single one with different offsets.
+   /**
+    * Image has multi-planar format and was created with
+    * VK_IMAGE_CREATE_DISJOINT_BIT.
     */
    bool disjoint;