tools/power turbostat: Warn on bad ACPI LPIT data

On some systems /sys/devices/system/cpu/cpuidle/low_power_idle_cpu_residency_us
or /sys/devices/system/cpu/cpuidle/low_power_idle_system_residency_us
return a file error because of bad ACPI LPIT data from a misconfigured BIOS.
turbostat interprets this failure as a fatal error and outputs

	turbostat: CPU LPI: No data available

If the ACPI LPIT sysfs files return an error output a warning instead of
a fatal error, disable the ACPI LPIT evaluation code, and continue.

Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: Len Brown <len.brown@intel.com>