perf tools: Read the cache line size lazily

It is not read as commonly as 'page_size', so it makes sense to read it
lazily, caching its value when it is first read.

Less files open unconditionally at startup.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-35xhrq91u94uc1djtclek1ie@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/util.h

@@ -43,7 +43,7 @@ size_t hex_width(u64 v);
 int hex2u64(const char *ptr, u64 *val);
 
 extern unsigned int page_size;
-extern int cacheline_size;
+int __pure cacheline_size(void);
 
 int fetch_kernel_version(unsigned int *puint,
 			 char *str, size_t str_sz);