mkfs.cramfs: reduce the synopsis to the standard, succinct form

mkfs.cramfs: reduce the synopsis to the standard, succinct form

The old synopsis was 1) incomplete (mentioning -h and -v, but not
-V and -E and -z, for example), and 2) overlong, being wider than
80 columns.  So, change the synposis to what most other utilities
nowadays use: "<name> [options] <arguments>..." -- this makes it
much clearer what the two required arguments are.

Also, reshuffle the descriptions of the two arguments, to not hide
them among the options.

And remove the description of option -s, as listing an option that
does nothing is not helpful.

Signed-off-by: Benno Schulenberg <bensberg@telfort.nl>