intel/blorp: Use isl_aux_usage_has_mcs instead of comparing

intel/blorp: Use isl_aux_usage_has_mcs instead of comparing

Depending on MCS_CSS or MCS we can emit blorp blit shaders.

As we support MCS_CSS and MCS, it makes sense to use
isl_aux_usage_has_mcs function.

v2: Fix commit message (Nanley Chery)

Signed-off-by: Sagar Ghuge <sagar.ghuge@intel.com>
Reviewed-by: Nanley Chery <nanley.g.chery@intel.com>