intel/isl: Require ISL_AUX_USAGE_HIZ_CCS_WT for HZ+CCS WT mode

intel/isl: Require ISL_AUX_USAGE_HIZ_CCS_WT for HZ+CCS WT mode

We also delete the badly named isl_surf_supports_hiz_ccs_wt.  The name
is misleading because it doesn't return whether or not the surface
supports HiZ+CCS in write-through mode (any single-sampled HiZ+CCS
capable surface does) but rather a heuristic decision about whether or
not we want to enable write-through mode based on the usage flags in the
isl_surf.

Reviewed-by: Nanley Chery <nanley.g.chery@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4056>