video: tegra: host: Restore poweroff request

video: tegra: host: Restore poweroff request

Change 1a1db66cc323f6ac9e1f0d95449078b8de2f0073 refactored
keepalive flag to take a real pm runtime reference to a
device whenever the corresponding device node was open.
However, this regressed suspend stress testing; Since we
now take a real pm runtime reference to the device, having
the device node open prevents suspend. Depending on timing,
this may lead to failure to suspend.

This patch restores the no-poweroff request functionality to
nvhost acm and modifies poweroff requests to be flushed.

Bug 200132609
Bug 200132870
Bug 1679106

Change-Id: Ibdabec9ee004f2724595c64736b1a36d7f2cff25
Signed-off-by: Arto Merilainen <amerilainen@nvidia.com>
Reviewed-on: http://git-master/r/791367
(cherry picked from commit 27019e0147b9a9b408b21fa530b3e50e6aa84881)
Reviewed-on: http://git-master/r/792513
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Charles Kong <charlesk@nvidia.com>
Reviewed-by: Shridhar Rasal <srasal@nvidia.com>