Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

Work around assembler error from clang 10.0.0 in gptboot:

stand/i386/gptboot/gptldr.S:141:3: error: value of 36878 is too large for field of 2 bytes.
jmp MEM_JMP # Start BTX
^

Use the same construct as in stand/i386/boot2/boot1.S, which ensures the
jump distance does not become too large.

MFC after: 3 days

Fix comments after bump in size.

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

Sponsored by: Netflix