[PATCH] powerpc: fix SMU driver interrupt mapping

The SMU driver tries to map an interrupt from the device-tree before the
interrupt controllers in the machine have been enumerated.  This doesn't work
properly and cause machines like the Quad g5 to fail booting later on when
some drivers waits endlessly for an SMU request to complete.  This is the
second problem preventing boot on the Quad g5.  This fixes it and also makes
the SMU driver a bit more resilient to not having an interrupt.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>