cpupower: change binding's makefile to use -lcpupower

cpupower: change binding's makefile to use -lcpupower

Originally I believed I needed the .o files to make the bindings. The
linking failed due to a missing .so link in Fedora or by using make
install-lib from the cpupower directory. Amend the makefile and the
README.

Big thanks to Wander Lairson Costa <wander@redhat.com> for the help.

Link: https://lore.kernel.org/r/20250429204711.127274-1-jwyatt@redhat.com
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>