tools/power turbostat: Build with _FILE_OFFSET_BITS=64

For compatibility reasons, Glibc off_t is a 32-bit type on 32-bit x86
unless _FILE_OFFSET_BITS=64 is defined. Add this define, as otherwise
reading MSRs with index 0x80000000 and above attempts a pread with a
negative offset, which fails.

Signed-off-by: Alexander Monakov <amonakov@ispras.ru>
Tested-by: Liwei Song <liwei.song@windriver.com>
Signed-off-by: Len Brown <len.brown@intel.com>