drm/i915: Prevent modesets during driver init/shutdown

drm/i915: Prevent modesets during driver init/shutdown

An unexpected modeset or connector detection by a user (user space or FB
console) during the initialization/shutdown sequence is possible either
via a hotplug IRQ handling work or via the connector sysfs
(status/detect) interface. These modesets/detections should be prevented
by disabling/flushing all related hotplug handling work and
unregistering the interfaces that can start them at the beginning of the
shutdown sequence. Some of this - disabling all related intel_hotplug
work - will be done by the next patch, but others - for instance
disabling the MST hotplug works - require a bigger rework.

It makes sense - for diagnostic purpose, even with all the above work and
interface disabled - to detect and reject any such user access. This
patch does that for modeset accesses and a follow-up patch for connector
detection.

During driver loading/unloading/system suspend/shutdown and during
system resume after calling intel_display_driver_disable_user_access()
or intel_display_driver_resume_access() correspondigly, the current
thread is allowed to modeset (as this thread requires to do an
initial/restoring modeset or a disabling modeset), other threads (the
user threads) are not allowed to modeset.

During driver loading/system resume after calling
intel_display_driver_enable_user_access() all threads are allowed to
modeset.

During driver unloading/system suspend/shutdown after calling
intel_display_driver_suspend_access() no threads are allowed to modeset
(as the HW got disabled and should stay in this state).

v2: Call intel_display_driver_suspend_access()/resume_access() only
    for HAS_DISPLAY(). (CI)
v3: (Jouni)
- Add commit log comments explaining how the permission of modeset
  changes during HW init/deinit wrt. to the current and other user
  processes.

Link: https://patchwork.freedesktop.org/patch/msgid/20240104132335.2766434-1-imre.deak@intel.com
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>