I don't have good method to you except copy tsntool binary to yocto:tiny rootfs manually.
1. $ flex-builder -c tsntool -a arm64
2. $ cp packages/apps/tsntool/tsntool build/rfs/rootfs_yocto_LS_arm64_tiny/target/usr/bin/
$cp packages/apps/tsntool/libtsn.so build/rfs/rootfs_yocto_LS_arm64_tiny/target/usr/lib
3. $ flex-builder -i packrfs -r yocto:tiny
