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Perform 1 drm commit consisting of all displays being modeset/disabled
together.
This guarantees that the kernel is aware of the states of all displays
at the same time, especially in case of inter-dependency.

ScreenManagerTest.{CheckForSecondValidController,CheckMultipleControllersAfterBeingDisabled}

BUG: b/172069469, b/168753412
TEST: modesetting kohaku with external display,
Change-Id: I4bb5b253eda793cc5807ab0000cc5e14854dc3d0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2551490Reviewed-by: Daniel Nicoara <dnicoara@chromium.org>
Commit-Queue: Mark Yacoub <markyacoub@google.com>
Cr-Commit-Position: refs/heads/master@{#843704}