arm: Use per-CPU irq_desc for PPIs and SGIs

arm: Use per-CPU irq_desc for PPIs and SGIs

The first 32 interrupts on a GIC are the Peripheral Private Interrupts
and Software-Generated Interrupts and are local to each processor.

The irq_desc cannot be shared since we use irq_desc->status to track
whether the IRQ is in-progress etc. Therefore give each processor its
own local irq_desc for each of these interupts.

We must also route them on each CPU, so do so.

This feels like a bit of a layering violation (since the core ARM
irq.c now knows about thinkgs wich are really gic.c business)

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Tim Deegan <tim@xen.org>
Committed-by: Ian Campbell <ian.campbell@citrix.com>