third_party/zephyr: Adapt atomic.h for EC build environment
third_party/zephyr: Adapt atomic.h for EC build environment

Remove unnecessary includes and redefinitions.

BUG=b:208435177
TEST=zmake testall & make buildall
BRANCH=none

Signed-off-by: Dawid Niedzwiecki <73bc8c219b84b29e82d4338ec2e55b540c845bc6@semihalf.com>
Change-Id: I50119ea67db6d7675b2cee6465b6bdccd14bc04a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3503668
Reviewed-by: Keith Short <f6d578f97033c25f1206cb57d52f358974c82954@chromium.org>
Commit-Queue: Dawid Niedzwiecki <f5bfc434019aa486188a171fe04a7dfcd4b6637d@google.com>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec