perf tools: Have the page size value available for all tools

Its such a common need that we might as well have a global with that
value.

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-mwfqji9f17k5j81l1404dk3q@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 8cdd232..15abe40 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -1375,15 +1375,13 @@
 {
 	u64 head, page_offset, file_offset, file_pos, progress_next;
 	int err, mmap_prot, mmap_flags, map_idx = 0;
-	size_t	page_size, mmap_size;
+	size_t	mmap_size;
 	char *buf, *mmaps[8];
 	union perf_event *event;
 	uint32_t size;
 
 	perf_tool__fill_defaults(tool);
 
-	page_size = sysconf(_SC_PAGESIZE);
-
 	page_offset = page_size * (data_offset / page_size);
 	file_offset = page_offset;
 	head = data_offset - page_offset;