tools/power turbostat: decode BXT TSC frequency via CPUID

Hard-code BXT ART to 19200MHz, so turbostat --debug
can fully enumerate TSC:

CPUID(0x15): eax_crystal: 3 ebx_tsc: 186 ecx_crystal_hz: 0
TSC: 1190 MHz (19200000 Hz * 186 / 3 / 1000000)

Signed-off-by: Len Brown <len.brown@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>