MPSAFE locking
MPSAFE locking

* Serialize operations in acpi_video_bind_outputs(), acpi_video_detach(),
  acpi_video_notify_handler(), acpi_video_power_profile(), and the sysctls.
  The main goal is to protect the shared device list and prevent conflicting
  settings.
* Add assertions that the sx lock is held in the leaf functions.

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