tools lib api fs: Introduce sysfs__read_{int,ull}()

To read either an int or an unsigned long long value from the given
file.

E.g.:

  $ cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq
  3200000
  $ ./sysfs__read_ull
  devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq
  /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq=3200000
  $

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-4a12m4d5k8m4qgc1vguocvei@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>