cpupower: Provide online and offline CPU information

When a user tries to modify cpuidle or cpufreq properties on offline
CPUs, the tool returns success (exit status 0) but also does not provide
any warning message regarding offline cpus that may have been specified
but left unchanged. In case of all or a few CPUs being offline, it can be
difficult to keep track of which CPUs didn't get the new frequency or idle
state set. Silent failures are difficult to keep track of when there are a
huge number of CPUs on which the action is performed.

This patch adds helper functions to find both online and offline CPUs and
print them out accordingly.

We use these helper functions in cpuidle-set and cpufreq-set to print an
additional message if the user attempts to modify offline cpus.

Reported-by: Pavithra R. Prakash <pavrampu@in.ibm.com>
Signed-off-by: Brahadambal Srinivasan <latha@linux.vnet.ibm.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>