intel/isl: Add a separate ISL_AUX_USAGE_STC_CCS

intel/isl: Add a separate ISL_AUX_USAGE_STC_CCS

Stencil CCS is slightly different from color CCS.  Using a color CCS
resolve with stencil CCS doesn't do the right thing and you can't sample
from a stencil CCS image without the DepthStencilResource bit set or you
will get the wrong data.  Stencil CCS also has it's own rules such as it
doesn't support fast-clear and has no partial resolve.  This seems to
indicate that it should probably be its own isl_aux_usage.  Now that
adding new isl_aux_usage values is pretty cheap, let's split stencil CCS
out on its own.

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