i965/fs: add support for BRW_OPCODE_AVG in fs_generator

Needed for compiling blorp blit programs.

Signed-off-by: Topi Pohjolainen <topi.pohjolainen@intel.com>
Reviewed-by: Paul Berry <stereotype441@gmail.com>

src/mesa/drivers/dri/i965/brw_fs_generator.cpp

@@ -1433,6 +1433,9 @@ fs_generator::generate_code(exec_list *instructions, FILE *dump_file)
       case BRW_OPCODE_MUL:
 	 brw_MUL(p, dst, src[0], src[1]);
 	 break;
+      case BRW_OPCODE_AVG:
+	 brw_AVG(p, dst, src[0], src[1]);
+	 break;
       case BRW_OPCODE_MACH:
 	 brw_set_acc_write_control(p, 1);
 	 brw_MACH(p, dst, src[0], src[1]);