powerpc/cpm2: Fix set interrupt type

This is a simple change to correct problems when using set_irq_type
on platforms using CPM2.  This code corrects the problem on most platform
but may have issues on 8272 derived platforms for some interrupts.

On 8272 PC2 & 3 are missing and PC 23 & 29 are added, which this patch
does not address.

Signed-off-by: Paul Bilke <paul@conspiracy.net>
Reviewed-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>