intel/eu: Encode and decode native instruction opcodes from/to IR opcodes.

intel/eu: Encode and decode native instruction opcodes from/to IR opcodes.

Change brw_inst_set_opcode() and brw_inst_opcode() to call
brw_opcode_encode/decode() transparently in order to translate between
hardware and IR opcodes, and update the EU compaction code in order to
do the same as needed, so we can eventually drop the one-to-one
correspondence between hardware and IR opcodes.

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>