Remove $FreeBSD$: two-line .h pattern

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

stand: Change disk_parsedev() API

Change the first argument to disk_parsedev() to be a pointer to a struct
devdesc *. This now gets filled in with a malloc'd structure that's
returned to the caller that the caller is repsonsible for freeing. Most
places in the tree passed in a malloc'd pointer anyway, and this moves
knowledge of disk_devdesc more firmly into the disk.[ch] code.

Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D37335

stand: Remove unused enum

enum disk_ioctl is unused. It's only ever defined. All of the stand
code uses DIOCGSECTORSIZE and DIOCGMEDIASIZE instead, both to query and
to implement ioctl.

Sponsored by: Netflix

stand: Change disk_fmtdev to take a struct devdesc *

We do a number of games with ploymorphism for different types struct
*devdesc. Adjust one place that this affects to take the address of the
base class (most others have void * at the moment). This is more type
safe than a bare void *.

Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D35914

Distinguish between "no partition" and "choose best partition" with a constant.

The values of the d_slice and d_partition fields of a disk_devdesc have a
few values with special meanings in the disk_open() routine. Through various
evolutions of the loader code over time, a d_partition value of -1 has
meant both "use the first ufs partition found in the bsd label" and "don't
open a bsd partition at all, open the raw slice."

This defines a new special value of -2 to mean open the raw slice, and it
gives symbolic names to all the special values used in d_slice and
d_partition, and adjusts all existing uses of those fields to use the new
constants.

The phab review for this timed out without being accepted, but I'm still
citing it below because there is useful commentary there.

Differential Revision: https://reviews.freebsd.org/D19262

Remove comments and assertions that are no longer valid after r330809.

r330809 replaced duplication of devdesc struct fields with an embedded copy
of the devdesc struct, to avoid fragility. That means all the scattered
comments indicating that structs must match are no longer valid. Likewise
asserts that attempted to mitigate some of the old fragility.

Reviewed by: imp@

Use the actual struct devdesc at the start of all *_devdesc structs

The current system is fragile and requires very careful layout of all
*_devdesc structures. It also makes it hard to change the base
devdesc. Take a page from CAM and put the 'header' in all the derived
classes and adjust the code to match.

For OFW, move the iHandle h_handle out of a slot conflicting with
d_opendata. Due to quirks in the alignment rules, this worked.
However changing the code to use d_opendata storage now that it's a
pointer is hard, so just have a separate field for it.

All other cleanups were to make the *_devdesc structures match where
they'd taken some liberties that were none-the-less compatible enough
to work.

Minor cosmetic changes.

Make sure { on the same line as struct for all struct *devdesc. Move
some type definitions to next to the dv_type define, since that's what
sets the d_type.

Move sys/boot to stand. Fix all references to new location

Sponsored by: Netflix