firewire: ohci: use threaded IRQ handler to handle SelfIDComplete event

firewire: ohci: use threaded IRQ handler to handle SelfIDComplete event

The first step  maintaining the bus topology is to handle SelfIDComplete
event. This event occurs after initiating bus reset when 1394 OHCI link
layer is enabled, or when the bus topology changes (e.g. when a device is
added). Because enumeration of the selfID sequence can take some time, it
should be processed in a bottom half.

Currently, this is done in a module-local workqueue with the
WQ_MEM_RECLAIM flag, to allow invocation during memory reclaim paths. A
threaded IRQ handler is a preferable alternative, as it eliminates the
need to manage workqueue attributes manually.

Although SelfIDComplete events are not so frequent in normal usage,
handling them correctly is critical for proper bus topology management.
This commit switches SelfIDComplete handling to a threaded IRQ handler.

Link: https://lore.kernel.org/r/20250823030954.268412-3-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>