libperf: Move 'page_size' global variable to libperf

We need the 'page_size' variable in libperf, so move it there.

Add a libperf_init() as a global libperf init function to obtain this
value via sysconf() at tool start.

Committer notes:

Add internal/lib.h to tools/perf/ files using 'page_size', sometimes
replacing util.h with it if that was the only reason for having util.h
included.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lore.kernel.org/lkml/20190913132355.21634-33-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/trace-event-info.c

@@ -2,7 +2,6 @@
 /*
  * Copyright (C) 2008,2009, Steven Rostedt <srostedt@redhat.com>
  */
-#include "util.h" // page_size
 #include <dirent.h>
 #include <mntent.h>
 #include <stdio.h>
@@ -19,6 +18,7 @@
 #include <linux/list.h>
 #include <linux/kernel.h>
 #include <linux/zalloc.h>
+#include <internal/lib.h> // page_size
 
 #include "trace-event.h"
 #include <api/fs/tracing_path.h>