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

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

Add define for CONST.

Newer interfaces take CONST parameters, so define CONST to minimize
differences between our headers and the standards docs.

Differential Revision: https://reviews.freebsd.org/D19971

loader.efi: efi variable rework and lsefi command added

This update does add diag and debug capabilities to interpret the efi
variables, configuration and protocols (lsefi).

The side effect is that we add/update bunch of related headers.

loader.efi: update memmap command to recognize new attributes

Also move memory type to string translation to libefi for later use.

MFC after: 2 weeks

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

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