PCI: Revert the cfg_access_lock lockdep mechanism

While the experiment did reveal that there are additional places that
are missing the lock during secondary bus reset, one of the places that
needs to take cfg_access_lock (pci_bus_lock()) is not prepared for
lockdep annotation.

Specifically, pci_bus_lock() takes pci_dev_lock() recursively and is
currently dependent on the fact that the device_lock() is marked
lockdep_set_novalidate_class(&dev->mutex). Otherwise, without that
annotation, pci_bus_lock() would need to use something like a new
pci_dev_lock_nested() helper, a scheme to track a PCI device's depth in
the topology, and a hope that the depth of a PCI tree never exceeds the
max value for a lockdep subclass.

The alternative to ripping out the lockdep coverage would be to deploy a
dynamic lock key for every PCI device. Unfortunately, there is evidence
that increasing the number of keys that lockdep needs to track to be
per-PCI-device is prohibitively expensive for something like the
cfg_access_lock.

The main motivation for adding the annotation in the first place was to
catch unlocked secondary bus resets, not necessarily catch lock ordering
problems between cfg_access_lock and other locks. Solve that narrower
problem with follow-on patches, and just due to targeted revert for now.

Fixes: 7e89efc6 ("PCI: Lock upstream bridge for pci_reset_function()")
Reported-by: Imre Deak <imre.deak@intel.com>
Closes: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_134186v1/shard-dg2-1/igt@device_reset@unbind-reset-rebind.html


Cc: Jani Saarinen <jani.saarinen@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
References: https://lore.kernel.org/all/ZlXP5oTnSApiDbD1@ideak-desk.fi.intel.com
References: #11223


Signed-off-by: Imre Deak <imre.deak@intel.com>
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240531183345.1400330-1-imre.deak@intel.com