loader: Retire CTASSERT

The project is moving away from CTASSERT in favor of
_Static_assert. Cleanup the few instances in the loader proactively.

Sponsored by: Netflix
Reviewed by: manu, tsoome
Differential Revision: https://reviews.freebsd.org/D44006

stand: Automated cleanup of cdefs and other formatting

Apply the following automated changes to try to eliminate
no-longer-needed sys/cdefs.h includes as well as now-empty
blank lines in a row.

Remove /^#if.*\n#endif.*\n#include\s+<sys/cdefs.h>.*\n/
Remove /\n+#include\s+<sys/cdefs.h>.*\n+#if.*\n#endif.*\n+/
Remove /\n+#if.*\n#endif.*\n+/
Remove /^#if.*\n#endif.*\n/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/types.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/param.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/capsicum.h>/

Sponsored by: Netflix

Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

stand/amd64: remove unused addr parameter from bi_load64

All callers of bi_load64 pass 0 as the addr parameter, so just remove
it and always calculate the last load address from the module chain.

No functional change.

Sponsored by: Citrix Systems R&D
Reviewed by: tsoome, imp
Differential revision: https://reviews.freebsd.org/D28412

stand/multiboot: adjust the protocol between loader and kernel

There's a currently ad-hoc protocol to hand off the FreeBSD kernel
payload between the loader and the kernel itself when Xen is in the
middle of the picture. Such protocol wasn't very resilient to changes
to the loader itself, because it relied on moving metadata around to
package it using a certain layout. This has proven to be fragile, so
replace it with a more robust version.

The new protocol requires using a xen_header structure that will be
used to pass data between the FreeBSD loader and the FreeBSD kernel
when booting in dom0 mode. At the moment the only data conveyed is the
offset of the start of the module metadata relative to the start of the
module itself.

This is a slightly disruptive change since it also requires a change
to the kernel which is contained in this patch. In order to update
with this change the kernel must be updated before updating the
loader, as described in the handbook. Note this is only required when
booting a FreeBSD/Xen dom0. This change doesn't affect the normal
FreeBSD boot protocol.

This fixes booting FreeBSD/Xen in dom0 mode after
3630506b9daec9167a89bc4525638ea45a00769e.

Sponsored by: Citrix Systems R&D
MFC after: 3 days
Reviewed by: tsoome
Differential Revision: https://reviews.freebsd.org/D28411

Prefer uintXX_t to u_intXX_t

A foolish consistency is the hobgoblin of little minds, adored by
little statesmen and philosophers and divines. With consistency a
great soul has simply nothing to do. -- Ralph Waldo Emerson

No need to use relative paths like this here.

Sponsored by: Netflix

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

Sponsored by: Netflix