intel/eu/gen12: Extend brw_inst.h macros for Gen12 support.

intel/eu/gen12: Extend brw_inst.h macros for Gen12 support.

The encoding of almost every instruction field has changed in Gen12,
so this involves adding a Gen12+ bitfield spec to every brw_inst
macro.  In addition some new macros are required to handle certain
discontiguous and variable-length fields.

This commit doesn't actually include the Gen12 updated bitfield specs,
only the macros are extended here for reviewability.

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
v2: Rename FDC() to FFDC() and FDC1() to FDC() for consistency with
    the existing F() and FF() macros.