[POWERPC] ps3: add interrupt alloc for outlets

PS3 interrupt core update:
  - Add ps3_alloc_irq() and ps3_free_irq(), to allocate a virtual interrupt
    number for an interrupt outlet, which is needed by the PS3 GPU frame
    buffer device and audio drivers

Signed-off-by: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Signed-off-by: Geoff Levand <geoffrey.levand@am.sony.com>
Acked-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>