arm/arm64: smp: add deadlock detection

on_cpu() and friends are a bit risky when implemented without IPIs
(no preemption), because we can easily get deadlocks. Luckily, it's
also easy to detect those deadlocks, and assert, to at least make
them easier to debug.

Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>