cpupower Makefile change to help run the tool without 'make install'

The cpupower tool, when compiled against libcpupower.so fail's to run as
the linker file path's are missing during compilation. So added changes
in the Makefile to run cpupower tool, which helps us run the tool
without doing a 'make install'.

Signed-off-by: Sriram Raghunathan <sriram@marirs.net.in>
Acked-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>