MFC r339703, r347365, r347703, r347940

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 as refined 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

r347365:
Update dme(4) to reflect that it will not be removed due to FCP-101.

dme(4) is the built-in NIC on a couple non-expandable mips platforms and
thus should remain. The FCP has been updated to reflect this fact.

Discussed with: imp

r347703:
FCP-101: ae(4) is sufficently popular to be moved to the keep list.

r347940:
Remove the notice that ae(4) will be removed in FreeBSD 13.

MFC requested by: rgrimes
Approved by: re (kib)