turbostat: Add a helper to parse a single int out of a file

Many different chunks of code in turbostat open a file, parse a single
int out of it, and close it.  Factor that out into a common function.

Signed-off-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Len Brown <len.brown@intel.com>

diff --cc tools/power/x86/turbostat/turbostat.c
Simple merge