anv: Fix VK_EXT_transform_feedback working with varyings packed in PSIZ

Transform feedback did not set correct SO_DECL.ComponentMask for
varyings packed in VARYING_SLOT_PSIZ:
 gl_Layer         - VARYING_SLOT_LAYER    in VARYING_SLOT_PSIZ.y
 gl_ViewportIndex - VARYING_SLOT_VIEWPORT in VARYING_SLOT_PSIZ.z
 gl_PointSize     - VARYING_SLOT_PSIZ     in VARYING_SLOT_PSIZ.w

Fixes: 36ee2fd61c "anv: Implement the basic form of VK_EXT_transform_feedback"

Signed-off-by: Danylo Piliaiev <danylo.piliaiev@globallogic.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

src/intel/vulkan/genX_pipeline.c

@@ -1211,13 +1211,30 @@ emit_3dstate_streamout(struct anv_pipeline *pipeline,
             hole_dwords -= 4;
          }
 
+         int varying = output->location;
+         uint8_t component_mask = output->component_mask;
+         /* VARYING_SLOT_PSIZ contains three scalar fields packed together:
+          * - VARYING_SLOT_LAYER    in VARYING_SLOT_PSIZ.y
+          * - VARYING_SLOT_VIEWPORT in VARYING_SLOT_PSIZ.z
+          * - VARYING_SLOT_PSIZ     in VARYING_SLOT_PSIZ.w
+          */
+         if (varying == VARYING_SLOT_LAYER) {
+            varying = VARYING_SLOT_PSIZ;
+            component_mask = 1 << 1; // SO_DECL_COMPMASK_Y
+         } else if (varying == VARYING_SLOT_VIEWPORT) {
+            varying = VARYING_SLOT_PSIZ;
+            component_mask = 1 << 2; // SO_DECL_COMPMASK_Z
+         } else if (varying == VARYING_SLOT_PSIZ) {
+            component_mask = 1 << 3; // SO_DECL_COMPMASK_W
+         }
+
          next_offset[buffer] = output->offset +
-                               __builtin_popcount(output->component_mask) * 4;
+                               __builtin_popcount(component_mask) * 4;
 
          so_decl[stream][decls[stream]++] = (struct GENX(SO_DECL)) {
             .OutputBufferSlot = buffer,
-            .RegisterIndex = vue_map->varying_to_slot[output->location],
-            .ComponentMask = output->component_mask,
+            .RegisterIndex = vue_map->varying_to_slot[varying],
+            .ComponentMask = component_mask,
          };
       }