sys: Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

mii: Add opt_platform.h to all miibus drivers

miivar.h includes opt_platform.h. Make sure all the drivers that use the
miibus_if.h interface file have opt_platform.h as well. While some of
these may not, strictly speaking, need it, it's easier to include it
universally for miibus.

Sponsored by: Netflix

sys/modules: normalize .CURDIR-relative paths to SRCTOP

This simplifies make output/logic

Tested with: `cd sys/modules; make ALL_MODULES=` on amd64
MFC after: 1 month
Sponsored by: Dell EMC Isilon

Build tsec(4) as a module.

Obtained from: Juniper Networks, Inc.