Some irqchips require IRQ affinity to be set from the context of the
migrated interrupt, such as Intel's IO*APIC hardware (see
CONFIG_GENERIC_PENDING_IRQ). Since the code actually changing the
affinity may be available to the in-band stage exclusively, we have to
defer its execution until events are synchronized for that stage
before returning from the interrupt frame.

Since we might have received the original event in a context from
which the in-band interrupt log will not be synchronized on top of
handle_irq_pipelined_finish(), we need a way to tag IRQ descriptors on
entry to the pipeline so that the flow handler won't schedule any
deferred affinity update for the event. Those contexts are:

- if the in-band stage is stalled
- if running on the out-of-band stage

IRQD_SETAFFINITY_BLOCKED is such a marker, telling the
architecture-specific pipeline code not to schedule any affinity
update when set.

Signed-off-by: Philippe Gerum <rpm@xenomai.org>