This is a followup to help address one of the omissions in the
threaded IRQ patches (v2) posted recently.  To recap, those
provided a quickcheck() routine that could wake an irq thread,
and a way to register a handler using that mechanism.

This addresses an orthogonal problem:  given some thread
demultiplexing the subsidiary IRQs reported to some top-level
interrupt, how can that kick in flow handlers chaining to
the subsidiary IRQs' handlers?

The answer here is more or less as suggested by Thomas:
using handle_threaded_irq(), a flow handler which doesn't
use handle_IRQ_event() since that doesn't much like being
called from thread context, at least when lockdep is active.

These two patches:

 - add handle_threaded_irq() flow handler;
 - kick it in for some twl4030 code

Tested on 2.6.29-rc8 code, both with and without the v2
irqthread patches.