tracing: Have function graph tracer define options per instance

Currently the function graph tracer's options are saved via a global mask
when it should be per instance. Use the new infrastructure to define a
"default_flags" field in the tracer structure that is used for the top
level instance as well as new ones.

Currently the global mask causes confusion:

# cd /sys/kernel/tracing
# mkdir instances/foo
# echo function_graph > instances/foo/current_tracer
# echo 1 > options/funcgraph-args
# echo function_graph > current_tracer
# cat trace
[..]
2) | _raw_spin_lock_irq(lock=0xffff96b97dea16c0) {
2) 0.422 us | do_raw_spin_lock(lock=0xffff96b97dea16c0);
7) | rcu_sched_clock_irq(user=0) {
2) 1.478 us | }
7) 0.758 us | rcu_is_cpu_rrupt_from_idle();
2) 0.647 us | enqueue_hrtimer(timer=0xffff96b97dea2058, base=0xffff96b97dea1740, mode=0);
# cat instances/foo/options/funcgraph-args
1
# cat instances/foo/trace
[..]
4) | __x64_sys_read() {
4) | ksys_read() {
4) 0.755 us | fdget_pos();
4) | vfs_read() {
4) | rw_verify_area() {
4) | security_file_permission() {
4) | apparmor_file_permission() {
4) | common_file_perm() {
4) | aa_file_perm() {
4) | rcu_read_lock_held() {
[..]

The above shows that updating the "funcgraph-args" option at the top level
instance also updates the "funcgraph-args" option in the instance but
because the update is only done by the instance that gets changed (as it
should), it's confusing to see that the option is already set in the other
instance.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: https://patch.msgid.link/20251111232429.641030027@kernel.org
Fixes: c132be2c4fcc1 ("function_graph: Have the instances use their own ftrace_ops for filtering")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>