Revert "PCI: Avoid reset when disabled via sysfs"

This reverts commit 479380ef.

The reset_method attribute on a PCI device is only intended to manage the
availability of function scoped resets for a device.  It was never intended
to restrict resets targeting the bus or slot.

In introducing a restriction that each device must support function level
reset by testing pci_reset_supported(), we essentially create a catch-22,
that a device must have a function scope reset in order to support bus/slot
reset, when we use bus/slot reset to effect a reset of a device that does
not support a function scoped reset, especially multi-function devices.

This breaks the majority of uses cases where vfio-pci uses bus/slot resets
to manage multifunction devices that do not support function scoped resets.

Fixes: 479380ef ("PCI: Avoid reset when disabled via sysfs")
Reported-by: Cal Peake <cp@absolutedigital.net>
Closes: https://lore.kernel.org/all/808e1111-27b7-f35b-6d5c-5b275e73677b@absolutedigital.net


Reported-by: Athul Krishna <athul.krishna.kr@protonmail.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220010


Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20250414211828.3530741-1-alex.williamson@redhat.com