Add per machine sysroot additions to /bin and /lib/onie

Allow machine definitions to place files into the final sysroot by
populating the following the directories under the machine root:

$MACHINEROOT/rootconf/sysroot-lib-onie ---> $SYROOT/lib/onie
$MACHINEROOT/rootconf/sysroot-bin      ---> $SYROOT/bin

This follows the same pattern used for CPU architecture specific
includes.