sys: Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

Mechanically convert if_xae to IfAPI

Reviewed by: zlei
Sponsored by: Juniper Networks, Inc.
Differential Revision: https://reviews.freebsd.org/D37797

Add driver for Xilinx AXI Ethernet tri-mode (10/100/1000 Mb/s) MAC found
in the U.S. Government Furnished Equipment (GFE) 64-bit RISC-V cores.

Sponsored by: DARPA, AFRL