tools/power x86_energy_perf_policy: Prefer driver HWP limits

When we are successful in using cpufreq min/max limits,
skip setting the raw MSR limits entirely.

This is necessary to avoid undoing any modification that
the cpufreq driver makes to our sysfs request.

eg. intel_pstate may take our request for a limit
that is valid according to HWP.CAP.MIN/MAX and clip
it to be within the range available in PLATFORM_INFO.

Signed-off-by: Len Brown <len.brown@intel.com>