firewire: core: add enumerator of self ID sequences and its KUnit test

firewire: core: add enumerator of self ID sequences and its KUnit test

When the state of bus reset finishes, 1394 OHCI driver constructs self ID
sequences, then it calls fw_core_handle_bus_reset() in core function. The
core function enumerates the self ID sequences to build bus topology.

This commit adds a structure and some helper functions for the enumeration,
and adds a KUnit test suite to ensure its expected behaviour.

Link: https://lore.kernel.org/r/20240605235155.116468-2-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>