In 1394 OHCI specification, the format of data for IT DMA is different from
the format of isochronous packet in IEEE 1394 specification, in its spd and
srcBusID fields.

This commit adds some static inline functions to serialize/deserialize the
data of IT DMA.

Link: https://lore.kernel.org/r/20240802003606.109402-4-o-takashi@sakamocchi.jpSigned-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>