Remove $FreeBSD$: two-line .h pattern

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

Break out the disk selection protocol from the rest of boot1.

Segregate the disk probing and selection protocol from the rest of the
boot loader.

Reviewed by: tsoome, bcran
Differential Revision: https://reviews.freebsd.org/D20547