anv: Rework the meaning of anv_image::planes[]::aux_usage

anv: Rework the meaning of anv_image::planes[]::aux_usage

Previously, we set aux_usage=ISL_AUX_USAGE_NONE when we really meant
CCS_D.  This sort-of made sense before we had anv_layout_to_aux_usage
but now that we have that helper.  However, in our more modern aux
tracking model, all aux usage goes through anv_layout_to_* and we're
better off making the meaning of anv_image::planes[]::aux_usage be
AUX_USAGE_NONE if and only if there is no compression.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3556>