Add IBM TS1160 density codes to libmt and the mt(1) man page.

These are taken directly from the density report from a TS1160
tape drive. (Using mt getdensity)

A TS1160 drive stores 20TB raw (60TB with compression) on a JE tape.

lib/libmt/mtlib.c:
Add 3592A6 encrypted/unencrypted density codes, and bpmm/bpi
values.

usr.bin/mt/mt.1:
Add 3592B5 encrypted/unencrypted density codes, bpmm/bpi
values and number of tracks. Bump the man page date.

MFC after: 3 days
Sponsored by: Spectra Logic