[PATCH] powerpc: enable irq's for platform functions.

Make the platform function interrupt functions actually work.  Calls
irq_enable() for the first in the list, and irq_disable() for the last.

Added *func to struct irq_client so the the user can pass just that to
pmf_unregister_irq_client().

Signed-off-by: Ben Collins <bcollins@ubuntu.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>