tools/power/turbostat: Fallback to an MSR read for EPB

Commit

  6d6501d9 ("tools/power/turbostat: Read energy_perf_bias from sysfs")

converted turbostat to read the energy_perf_bias value from sysfs.
However, older kernels which do not have that file yet, would fail. For
those, fall back to the MSR reading.

Fixes: 6d6501d9

 ("tools/power/turbostat: Read energy_perf_bias from sysfs")
Reported-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Tested-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Link: https://lkml.kernel.org/r/20210127132444.981120-1-dedekind1@gmail.com