config: enable ftrace features on all flavors
    
    We enable the following function tracing options:
    - FUNCTION_TRACER
    - DYNAMIC_FTRACE
    - FUNCTION_PROFILER
    - FUNCTION_GRAPH_TRACER
    
    With dynamic ftrace, there is very little runtime overhead.
    
    FUNCTION_GRAPH_TRACER is disabled only on ARM because it enables
    frame pointers there, so there is a real runtime cost even when it
    is disabled.