cpupower: fix lib default installation path

Invocation the tool built with the default settings fails:
$ cpupower
cpupower: error while loading shared libraries: libcpupower.so.1: cannot
open shared object file: No such file or directory

The issue is that Makefile puts the library to "/usr/lib64" dir for a 64
bit machine. This is wrong. According to the "File hierarchy standard
specification:
https://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard
https://refspecs.linuxfoundation.org/FHS_3.0/fhs-3.0.pdf



"/usr/lib<qual>" dirs are intended for alternative-format libraries
(e.g., "/usr/lib32" for 32-bit libraries on a 64-bit machine (optional)).

The utility is built for the current machine and doesn't handle
'CROSS_COMPILE' and 'ARCH' env variables. It also doesn't change bit
depth. So the result is always the same - binary for x86_64
architecture. Therefore the library should be put in the '/usr/lib'
dir regardless of the build options.
This is the case for all the distros that comply with the
'File Hierarchy Standard 3.0" by Linux Foundation. Most of the distros
comply with it. For example, one can check this by examining the
"/usr/lb64" dir on debian-based distros and find that it contains only
"/usr/lib64/ld-linux-x86-64.so.2". And examine that "/usr/lib" contains
both 32 and 64 bit code:
find /usr/lib -name "*.so*" -type f | xargs file | grep 32-bit
find /usr/lib -name "*.so*" -type f | xargs file | grep 64-bit

Fix the issue by changing library destination dir to "/usr/lib".

Signed-off-by: Roman Storozhenko <romeusmeister@gmail.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>