lifecycle.c

When interrupts are disabled during API calls on core 1, we can only
trigger a core 1 reset when there is no API call ongoing.  This means
that the lifecycle machinery needs to allow any running API calls to
complete before it has a chance to see its reset interrupt delivered.

This is complicated because we cannot synchronize on core 1 triggering
an API call - the best we can do is stop the dispatcher, check whether
our reset interrupt was delivered, and if not, give it another chance to
process an API call.

Additionally, "give it another chance to process an API call" means that
the IDLE task must run, because this is currently a prerequisite to
scheduling the dispatcher (see [1]).  The only way to facilitate this is
with a sleep that is long enough that it will eventually let core 0 go
idle.  It seems that an 8 tick delay does the job quite fine.

Thus, implement a busy loop which provides the above requirements and
with that makes Epicardium prepared for payloads which perform API calls
with interrupts disabled.

[1]: https://firmware.card10.badge.events.ccc.de/epicardium/overview.html#internals