copy-firmware: fail gracefully if moreutils parallel is installed

copy-firmware: fail gracefully if moreutils parallel is installed

The copy-firmware.sh script can use the "parallel" command to
parallelize some operations, but it needs the GNU version of
parallel.  There is another, simpler version of parallel that is part
of the moreutils package, but that version confuses the
has_gnu_parallel() function.  So first test to make sure that
the --version parameter is even recognized before trying to use it.

If in the future, moreutils parallel adds support for --version, this
script should still work because that version should never report
"GNU parallel".

Signed-off-by: Timur Tabi <ttabi@nvidia.com>