Fix the 'linux' rc script on aarch64.

Previously it would try to load linux.ko instead of linux64.ko
and fail. While here, don't try to match 'linuxaout'; even if
implemented, it's the same module as linuxelf.

Reviewed By: emaste
Sponsored By: EPSRC
Differential Revision: https://reviews.freebsd.org/D29288

(cherry picked from commit e026f4243c5a65d19a63d98f55be17e8294a1e87)