add timestamp intp function tracing

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@gmail.com>
introduce print_trace_clock built-in function

This function is useful for print value of current tracing clock
which used by ring buffer.

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@gmail.com>
print timestamp only if -T option is given

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@gmail.com>
fix the coding style issue

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@gmail.com>
remove trace_end in scripts/syscalls.kp

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@gmail.com>
update ktap command usage text

support -o FILE option soon.

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@gmail.com>
support event filter

Simple example on function filter:

trace "ftrace:function /ip==mutex*/" function (e) {
	print(e)
}

ftrace_profile_set_filter need to export in future.

One issue about filter: event filter is added(ftrace_profile_set_filter)
after event created(perf_event_create_kernel_counter),
this will cause there have many event unfilted output into
ringbuffer before set filter. This issue need more review,
perhaps need fix in perf core code in mainline.

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@gmail.com>