MFC r339703:

Deprecate a number of less used 10 and 10/100 Ethernet devices.

The current deprecated list is: ae, bm, cs, de, dme, ed, ep, ex, fe,
pcn, sf, sn, tl, tx, txp, vx, wb, xe

The list was defined as part of FCP-0101. Per the FCP, devices may be
removed from the deprecation list if enough users are found or they are
converted to iflib.

FCP: https://github.com/freebsd/fcp/blob/master/fcp-0101.md
Approved by: re (gjb)
Reviewed by: rgrimes
Differential Revision: https://reviews.freebsd.org/D17654