libsa: Remove redundant sys/cdefs.h

Sponsored by: Netflix

Remove $FreeBSD$: one-line .c pattern

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

stand: Use c99 structure initialization for gzipfs_fsops

Sponsored by: Netflix

libsa: Fix infinite loop in bzipfs & gzipfs

A bug in the loader's bzipfs & gzipfs filesystems caused compressed
kernel and modules not to work on EFI systems with a veriexec-enabled
loader. Since the size of files in these filesystems are not known
_a priori_ `stat` would initialize the size to -1 and the loader would
then hang in an infinite loop while trying to seek (read) to the end
of file since the loop termination condition compares the current
offset to that negative target position.

Reviewers: vangyzen, imp, Bret Ketchum (Bret.Ketchum@dell.com)
Differential Revision: https://reviews.freebsd.org/D30414
Sponsored by: Dell EMC Isilon
MFC to: stable/12, stable/13
MFC after: 1 week

libsa: gzipfs.c converts pointers to integer types with different sign

Signed versus unsigned char.

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

Sponsored by: Netflix