The Cache Manager directives are available via <rtems.h>. Document most
of them in the Classic API Guide.
Not documented are the following directive since the API is not yet
stable:
* rtems_cache_coherent_allocate()
* rtems_cache_coherent_free()
* rtems_cache_coherent_add_area()
Not documented are the following directive since the directives are not
implemented on maintained platforms:
* rtems_cache_freeze_data()
* rtems_cache_freeze_instruction()
* rtems_cache_unfreeze_data()
* rtems_cache_unfreeze_instruction()
Close#4513.
