pm:cpupower: Add error warning when SWIG is not installed

Add error message to better explain to the user when SWIG and
python-config is missing from the path. Makefile was cleaned up
and unneeded elements were removed.

Suggested-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: John B. Wyatt IV <jwyatt@redhat.com>
Signed-off-by: John B. Wyatt IV <sageofredondo@gmail.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>