stand/efi: Consolidate integer types

We have no need for 5 different copies of these.

Sponsored by: Netflix
Reviewed by: rcm, kevans, andrew
Differential Revision: https://reviews.freebsd.org/D42699

Remove $FreeBSD$: one-line .c comment pattern

Remove /^/[*/]\s*\$FreeBSD\$.*\n/

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

Sponsored by: Netflix