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

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

Add an elf not so kgdb detects the kernel as a FreeBSD elf file. The
ELFNOTE macro is based on one from the FreeBSD/ARM Xen tree [1].

Obtained from: Julien Grall <julien.grall AT linaro.org> [1]