radv: implement PS epilogs

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17485>

src/amd/vulkan/radv_shader_args.c

@@ -450,6 +450,12 @@ declare_ps_input_vgprs(const struct radv_shader_info *info, struct radv_shader_a
          vgpr_arg++;
       }
    }
+
+   if (info->ps.has_epilog) {
+      /* FIXME: Ensure the main shader doesn't have less VGPRs than the epilog */
+      for (unsigned i = 0; i < MAX_RTS; i++)
+         ac_add_arg(&args->ac, AC_ARG_VGPR, 4, AC_ARG_INT, NULL);
+   }
 }
 
 static void