Remove $FreeBSD$: one-line sh pattern

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

dma: make the version exposed reflect the new version

libexec: normalize paths using SRCTOP-relative paths or :H when possible

This simplifies make logic/output

MFC after: 1 month
Sponsored by: Dell EMC Isilon

Do not override top level CFLAGS in libexec/dma

Create a dedicated package for dma

Move all the dma(8) components into one single directory

Simplifying maintainance and options (only one place to deal with MK_DMAGENT)

This also makes packaging base less intrusive by getting a single point where
to add tags.