probe_event_enable/disable() check tu->consumer != NULL to avoid the
wrong uprobe_register/unregister().
We are going to kill this pointer and "struct uprobe_trace_consumer",
so we add the new helper, is_trace_uprobe_enabled(), which can rely
on TP_FLAG_TRACE/TP_FLAG_PROFILE instead.
Note: the current logic doesn't look optimal, it is not clear why
TP_FLAG_TRACE/TP_FLAG_PROFILE are mutually exclusive, we will probably
change this later.