Blackfin: fix deadlock in SMP IPI handler

When a low priority interrupt (like ethernet) is triggered between 2 high
priority IPI messages, a deadlock in disable_irq() is hit by the second
IPI handler.  This is because the second IPI message is queued within the
first IPI handler, but the handler doesn't process all messages, and new
ones are inserted rather than appended.  So now we process all the pending
messages, and append new ones to the pending list.

URL: http://blackfin.uclinux.org/gf/tracker/5226


Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>