i965/miptree: Replace is_lossless_compressed with mt->aux_usage checks

i965/miptree: Replace is_lossless_compressed with mt->aux_usage checks

Now that we have an actual aux_usage field, we no longer need the
complex logic of is_lossless_compressed in order to figure out if a
miptree is CCS_E compressed.  As a side-effect, there is not longer any
need to overload MSAA_LAYOUT_CMS for CCS_E and we can stop doing so.

Reviewed-by: Chad Versace <chadversary@chromium.org>
Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>