intel: Rename the GFX12_CCS_E aux-usage to FCV_CCS_E

intel: Rename the GFX12_CCS_E aux-usage to FCV_CCS_E

Rename the isl_aux_usage enum to clarify that it is optional on gfx125.

The new name comes from the Alchemist docs, where the feature is
referred to as "Fast Clear Optimization (FCV)".

The rename was done with this command:

   git grep -l "GFX12_CCS_E" | xargs sed -ie "s/GFX12_CCS_E/FCV_CCS_E/g"

Reviewed-by: Rohan Garg <rohan.garg@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23220>