cpupower : Auto-completion for cpupower tool

This script adds support for auto-completion for cpupower tool.
Added support for auto-completion of all the eight commands for
cpupower tool and their all subsequent sub-commands, wherever
possible.

A sample output after applying this script -

root@ubuntu:~# cpupower f<TAB>
root@ubuntu:~# cpupower frequency-<TAB>
frequency-info  frequency-set
root@ubuntu:~# cpupower frequency-set -
-d          --freq      --governor  --min       --related
-f          -g          --max       -r          -u
root@ubuntu:~# cpupower frequency-set -g <TAB>
conservative ondemand performance powersave schedutil userspace
root@ubuntu:~# cpupower frequency-set -f <TAB>
2061000  2194000  2327000  2460000  2593000  2726000  2859000
2094000  2227000  2360000  2493000  2626000  2759000  2892000
2128000  2261000  2394000  2527000  2660000  2793000  2926000
2161000  2294000  2427000  2560000  2693000  2826000  2959000
root@ubuntu:~# cpupower frequency-set -f 206<TAB>
root@ubuntu:~# cpupower frequency-set -f 2061000

Signed-off-by: Abhishek Goel <huntbag@linux.vnet.ibm.com>
Signed-off-by: Bharath Thodla <bharath.thodla@in.ibm.com>
Tested-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Shuah Khan <shuah@kernel.org>