fgraph: Change the name of cpuhp state to "fgraph:online"

The cpuhp state name given to cpuhp_setup_state() is "fgraph_idle_init"
which doesn't really conform to the names that are used for cpu hotplug
setups. Instead rename it to "fgraph:online" to be in line with other
states.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/20241024222944.473d88c5@rorschach.local.home


Suggested-by: Masami Hiramatsu <mhiramat@kernel.org>
Fixes: 2c02f737 ("fgraph: Use CPU hotplug mechanism to initialize idle shadow stacks")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>