Add KMS Atomic Commit option to null_platform_test

Run null_platform_test using KMS Atomic APIs instead. If the device
does not have atomic capabilities, it will fallback to use legacy APIs.
Added Atomic helper API to bsdrm/src/kms.c, can be included from bs_drm.h

BUG=None
TEST=None

Change-Id: I7419934f85e85353374405b6c3ec2c358c871c79
Reviewed-on: https://chromium-review.googlesource.com/1626467
Tested-by: Mark Yacoub <markyacoub@google.com>
Commit-Ready: Mark Yacoub <markyacoub@google.com>
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Daniele Castagna <dcastagna@chromium.org>
Reviewed-by: Mark Yacoub <markyacoub@google.com>
3 files changed