intel/isl: Add an enum for describing auxiliary compression state

intel/isl: Add an enum for describing auxiliary compression state

This enum describes all of the states that a auxiliary compressed
surface can have.  All of the states as well as normative language for
referring to each of the compression operations is provided in the
truly colossal comment for the new isl_aux_state enum.  There is also
a diagram showing how surfaces move between the different states.

Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>
Reviewed-by: Nanley Chery <nanley.g.chery@intel.com>
Reviewed-by: Chad Versace <chadversary@chromium.org>