tools/blobtool: Always autodetect compression on tarball unpack
tools/blobtool: Always autodetect compression on tarball unpack

- Don't allow the user to override the compression algorithm when
unpacking a tarball; always autodetect

- Update usage message accordingly

- Add checks for invalid uses of --compression parameter

cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr