make: Compile with libpmem if --with-pmdk is set.

Signed-off-by: Maciej Szczepaniak <maciej.szczepaniak@intel.com>
Change-Id: I120c4a1e04df5cf79900b6b84d7392f57ca25238
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/648


Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Reviewed-by: Konrad Sztyber <konrad.sztyber@intel.com>
Reviewed-by: Wojciech Malikowski <wojciech.malikowski@intel.com>