tools/power/x86/intel-speed-select: Make target CPU optional for core-power info

Currently "-c" is a mandatory option for "core-power info" command. Make
this optional as this is a per package/die property. When not specified,
it will print info for every package/die.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>