iris: Add restriction to 3DSTATE_CONSTANT_ packets.

The following programming note shows up in all 3DSTATE_CONSTANT_*
packets:

   "The sum of all four read length fields must be less than or equal to
   the size of 64."

The backend compiler should guarantee this for us, so let's just add a
check here.

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>

src/gallium/drivers/iris/iris_state.c

@@ -5108,6 +5108,8 @@ setup_constant_buffers(struct iris_context *ice,
    struct iris_compiled_shader *shader = ice->shaders.prog[stage];
    struct brw_stage_prog_data *prog_data = (void *) shader->prog_data;
 
+   uint32_t push_range_sum = 0;
+
    int n = 0;
    for (int i = 0; i < 4; i++) {
       const struct brw_ubo_range *range = &prog_data->ubo_ranges[i];
@@ -5115,6 +5117,8 @@ setup_constant_buffers(struct iris_context *ice,
       if (range->length == 0)
          continue;
 
+      push_range_sum += range->length;
+
       if (range->length > push_bos->max_length)
          push_bos->max_length = range->length;
 
@@ -5135,6 +5139,13 @@ setup_constant_buffers(struct iris_context *ice,
       n++;
    }
 
+   /* From the 3DSTATE_CONSTANT_XS and 3DSTATE_CONSTANT_ALL programming notes:
+    *
+    *    "The sum of all four read length fields must be less than or
+    *    equal to the size of 64."
+    */
+   assert(push_range_sum <= 64);
+
    push_bos->buffer_count = n;
 }