MFC r326276:

various: general adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using misidentified many licenses so this was mostly a manual - error
prone - task.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

No functional change intended.

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Fix world after byacc import:
- old yacc(1) use to magicially append stdlib.h, while new one don't
- new yacc(1) do declare yyparse by itself, fix redundant declaration of
'yyparse'

Approved by: des (mentor)

Add the ability to match the on a media type of the device in question.

Submitted by: sam
Approved by: re (scottl)

Parse the ! lines that will soon be coming from the kernel. These are
a generalized notification mechanism for subsystems wishing to report
events.

Revieded by: njl

# The kernel side seems like it might be causing panics for me, but should
# be forthcoming shortly.

Allow zero or more actions in an action list, rather than requiring
one or more actions in the list. This makes constructs like:

attach 10 {
// echo "Driver $device_name attached"
};

to be accepted by the parser. It will be treated as if the user had
entered:

// attach 10 {
// echo "Driver $device_name attached"
// };

(eg totally ignored).

Approved by: re@ (rwatson)

MFp4 (imp_freebsd branch): snapshot of devd work:
o improve parsing and lexing
o create data structures based on the parsed file now.
o Still need to rewrite main loop and add regex (still uses hard coded
devd-generic)
o minor man page updates.

# There should be one more commit before rc2

Approved by: re (blanket)

devd. A daemon that hooks into the kernel's /dev/devctl to produce
arbitrary commands when devices come and go in the device tree (which is
different than the /dev directory).

This is an initial version. Much of the planned power isn't here.
Instead of doing the full matching, we always run /etc/devd-generic.
/etc/devd.generic will go away at some point, I think.

I'm committing it in this early state so I can start getting feedback
from early adapters.

Approved by: re