firewire: core: add tracepoints events for starting/stopping of isochronous context

It is helpful to trace the starting and stopping of isochronous context
when the core function is requested them by both in-kernel unit drivers
and userspace applications.

This commit adds some tracepoints events for the aim.

Link: https://lore.kernel.org/r/20240623220859.851685-4-o-takashi@sakamocchi.jp


Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>