iris: Enable HiZ for multisampled depth surfaces.

iris: Enable HiZ for multisampled depth surfaces.

Fix this check so that we can get a HiZ aux buffer for multisampled
surfaces as well. Also make sure we don't try to emit a sampler view
surface state for multisampled depth sufaces with HiZ enabled, as
the sampler can't HiZ for multisampled buffers and isl would assert.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>