sfdisk: add --unit and --show-geometry, update deprecated.txt

Signed-off-by: Karel Zak <kzak@redhat.com>
sfdisk: add --quiet

Note that original sfdisk implementation suppressed warning
messages for --quiet.

Now we keep warning and error messages visible, but suppress
extra info messages only (for example to make it more usable in
scripts). IMHO suppress warnings is bad idea.

Signed-off-by: Karel Zak <kzak@redhat.com>