tracing/selftests: Update kprobe args char/string to match new functions

The function that the kprobe_args_char and kprobes_arg_string attaches to
for its test has changed its name once again. Now we need to check for
eventfs_create_dir(), and if it exists, use that, otherwise check for
eventfs_add_dir() and if that exists use that, otherwise use the original
tracefs_create_dir()!

Link: https://lore.kernel.org/linux-trace-kernel/20230914163535.487267410@goodmis.org

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Ajay Kaher <akaher@vmware.com>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>