intel/compiler: Silence unused parameter warnings in brw_eu.h

intel/compiler: Silence unused parameter warnings in brw_eu.h

All of the other brw_*_desc functions take a devinfo parameter, and all
of the others at least have an assert that uses it.  Keep the parameter,
but mark it as unused.

Silences 37 warnings like:

In file included from src/intel/common/gen_disasm.c:27:0:
src/intel/compiler/brw_eu.h: In function ‘brw_pixel_interp_desc’:
src/intel/compiler/brw_eu.h:377:53: warning: unused parameter ‘devinfo’ [-Wunused-parameter]
 brw_pixel_interp_desc(const struct gen_device_info *devinfo,
                                                     ^~~~~~~

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>