tools/power turbostat: add --cpu parameter

With the --cpu parameter, turbostat prints only lines
for the specified set of CPUs:

sudo ./turbostat --quiet --show Core,CPU --cpu 0,1,3..5,6-7
	Core	CPU
	-	-
	0	0
	0	4
	1	1
	1	5
	2	6
	3	3
	3	7

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