broadcom/compiler: check if vertex shader writes point size

The same we already check for geometry shaders. We will use this
shortly.

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/29413>

src/broadcom/compiler/v3d_compiler.h

@@ -986,6 +986,8 @@ struct v3d_vs_prog_data {
         /* Value to be programmed in VCM_CACHE_SIZE. */
         uint8_t vcm_cache_size;
 
+        bool writes_psiz;
+
         /* Maps the nir->data.location to its
          * nir->data.driver_location. In general we are using the
          * driver location as index (like vattr_sizes above), so this

src/broadcom/compiler/vir.c

@@ -792,6 +792,9 @@ v3d_vs_set_prog_data(struct v3d_compile *c,
         if (prog_data->uses_iid)
                 prog_data->vpm_input_size++;
 
+        prog_data->writes_psiz =
+            c->s->info.outputs_written & (1 << VARYING_SLOT_PSIZ);
+
         /* Input/output segment size are in sectors (8 rows of 32 bits per
          * channel).
          */