tools lib traceevent, perf tools: Split trace-seq related APIs in a separate header file

In order to make libtraceevent into a proper library, all its APIs
should be defined in corresponding header files.  This patch splits
trace-seq related APIs in a separate header file: trace-seq.h

Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/20180828185038.2dcb2743@gandalf.local.home


Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>