tracing: Have syscall tracing call its own init function

In the clean up of having all events call one specific function,
the syscall event init was changed to call this helper function.

With the new print_fmt updates, the syscalls need to do special
initializations. This patch converts the syscall events to call
its own init function again.

Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>