firewire: ohci: add static inline functions to deserialize for Self-ID DMA operation

firewire: ohci: add static inline functions to deserialize for Self-ID DMA operation

The SelfI-ID is one type of DMAs defined in 1394 OHCI specification. It is
operated by two registers, one interrupt, and has one format of buffer.

This commit adds some static inline functions to deserialize the data in
the buffer and registers. Some KUnit tests are also added to check their
reliability.

Link: https://lore.kernel.org/r/20240702222034.1378764-4-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>