From the Vulkan spec:
    "VK_IMAGE_LAYOUT_DEPTH_STENCIL_READ_ONLY_OPTIMAL specifies a
     layout for both the depth and stencil aspects of a depth/stencil
     format image allowing read only access as a depth/stencil
     attachment or in shaders as a sampled image, combined
     image/sampler, or input attachment. It is equivalent to
     VK_IMAGE_LAYOUT_DEPTH_READ_ONLY_OPTIMAL and
     VK_IMAGE_LAYOUT_STENCIL_READ_ONLY_OPTIMAL."

So, it should be safe to keep HTILE compressed if the depth/stencil
image isn't going to be sampled. We could probably extend this
to separate depth/stencil layout but that seems a bit more
complicated.

This gives a huge boost to the deferredmultisampling Vulkan demo.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Part-of: <!10008>