[POWERPC] Fix CDS IRQ handling and PCI code

* Fix IRQ support in the 85xx CDS boards so it uses the new
  generic stuff
* Fix PCI IRQ mapping to use the device tree
* Disabled i8259 support to allow the CDS to boot.  This will be
  fixed soon, but the current code doesn't even compile, so this
  is a vast improvement

Signed-off-by: Andy Fleming <afleming@freescale.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>