tracing: have latency tracers set the latency format

The latency tracers (irqsoff, preemptoff, preemptirqsoff, and wakeup)
are pretty useless with the default output format. This patch makes them
automatically enable the latency format when they are selected. They
also record the state of the latency option, and if it was not enabled
when selected, they disable it on reset.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>