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: update prototypes for md_load and md_load64

These are declared as extern in a number of files (some with the wrong
return type). Centralize this in modinfo.h and remove a few extra stray
declarations as well that are no longer used. No functional change.

Note: I've not tried to cope with the bi_load() functions which are the
same logical thing. These will be handled separately.

Sponsored by: Netflix

[PowerPC64] stand: fix build using clang 8 as compiler

This change fixes "stand" build issues when using clang 8
as compiler.

Submitted by: alfredo.junior_eldorado.org.br
Reviewed by: jhibbits
Differential Revision: https://reviews.freebsd.org/D20026

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

Move "common" Open Firmware parts of the loader used only on PowerPC to
the powerpc/ subdirectory. These have never used by SPARC and we have
no other (and almost certainly will have no other) Open Firmware platforms.
This makes the directory structure simpler and lets us avoid some
cargo-cult MI patterns on code that is, and always was,
architecture-specific.