tools lib traceevent: Hide non API functions

There are internal library functions, which are not declared as a static.
They are used inside the library from different files. Hide them from
the library users, as they are not part of the API.
These functions are made hidden and are renamed without the prefix "tep_":
 tep_free_plugin_paths
 tep_peek_char
 tep_buffer_init
 tep_get_input_buf_ptr
 tep_get_input_buf
 tep_read_token
 tep_free_token
 tep_free_event
 tep_free_format_field
 __tep_parse_format

Link: https://lore.kernel.org/linux-trace-devel/e4afdd82deb5e023d53231bb13e08dca78085fb0.camel@decadent.org.uk/
Reported-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: linux-trace-devel@vger.kernel.org
Link: http://lore.kernel.org/lkml/20200930110733.280534-1-tz.stoyanov@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>