cmake: use libdir macros

cmake: use libdir macros

Don't hardcode ${prefix}/lib. More better give choice to maintainer where install libs.
We will use ${LIB_INSTALL_DIR}, which by default will point to
${CMAKE_INSTALL_PREFIX}/lib. But maintainer will can redefine it with
-DLIB_INSTALL_DIR=/usr/lib64 or the same.
Let's use libdir macroses.

Signed-off-by: Igor Gnatenko <i.gnatenko.brain@gmail.com>
Reviewed-by: Zhigang Gong <zhigang.gong@linux.intel.com>