Add IBM TS1170 density codes and specs.

These were obtained from a drive, but they agree with the IBM
documentation.

The bpi/bpmm values are the same as TS1160, but the number of
tracks is much larger (18944 tracks vs 8704 for TS1160). The tapes
are also longer, 1337m total. (According to the MAM on a sample JF
tape. I don't have a JE tape handy to compare.) The end result
is a 50TB raw capacity (150TB compressed) for TS1170 with a JF
cartridge vs 20TB raw capacity (60TB compressed) for TS1160 with
a JE cartridge.

lib/libmt/mtlib.c:
Add the TS1170 density codes to the denstiy table in libmt.

usr.bin/mt/mt.1:
Add the TS1170 density codes and specs to the density table
in the mt(1) man page. As usual for TS drives, there is an
encrypted and non-encrypted density code (0x79 and 0x59
respectively).

Sponsored by: Spectra Logic

(cherry picked from commit 83823d063ab57db8d3954c1530d036f1ccdceb41)