intel/ir: Drop hard-coded correspondence between IR and HW opcodes.

intel/ir: Drop hard-coded correspondence between IR and HW opcodes.

Having the IR opcodes locked to their hardware representation is risky
because it causes opcodes as different as BRC and IFF to compare equal
at the IR level (luckily the back-end only ever uses one opcode from
each group, right now), and it prevents us from supporting
instructions that change their hardware representation across
generations, which will become a problem on Gen12+ platforms.

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>