Refer to DSV in 'pstore import'

Drop explicit references to CSV in the source code as the input format
can be TSV or some other tabular text format besides CSV.

Signed-off-by: Jussi Virtanen <jussi.k.virtanen@gmail.com>
Rename 'gencsv' to 'gendsv'

It can generate both CSV and TSV files.

Signed-off-by: Jussi Virtanen <jussi.k.virtanen@gmail.com>
Deduce format from filename in 'gendsv'

If the extension is '.tsv', use a tab character as the separator.
Otherwise use a comma as the separator.

Signed-off-by: Jussi Virtanen <jussi.k.virtanen@gmail.com>