purge asm/atomic.h usage

We've never really guaranteed that this code works in a multithreaded
setup, and the only two users of this code are single threaded (`verity`
and `cros_installer`).  So simplify the atomic_t logic by inlining it
all and then dump the support code.

BUG=chromium:878440
TEST=build works

Change-Id: I5fb95c5623b937e930dac00d37edcb7effdada64
Reviewed-on: https://chromium-review.googlesource.com/1201402
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
6 files changed