tools/power turbostat: Build-in "Low Power Idle" counters support

Linux 4.15 exports the ACPI Low Power Idle Table's
counters in /sys/devices/system/cpu/cpuidle/

low_power_idle_cpu_residency_us

	Show this in the "CPU%LPI" column.

	Today this reflects the "North Complex"
	residency in PC10, so expect it to
	closely follow "Pk%pc10".

low_power_idle_system_residency_us

	Show this in the "SYS%LPI" column.

	Today, this reflects the North is in PC10,
	plus the PCH is sufficiently quiescent
	to save additional power via the "S0ix"
	system state, as measured by the
	PCH SLP_S0 counter.

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