linux: fix architecture returned for uname on aarch64

Previously it would return "arm64", which was breaking build
for Linux kernel. While here, reshuffle entries in the auxv
vector to match real Linux.

Reviewed By: emaste
Sponsored By: EPSRC
Differential Revision: https://reviews.freebsd.org/D30500

(cherry picked from commit aa462cab60c8957a97f612d36ac0a4dfa501bbbe)