openpic: add some bounds checking for IRQ numbers

The two checks with abort() guard against potential QEMU-internal
problems, but the EOI check stops the guest from causing updates to queue
position -1 and other havoc if it writes EOI with no interrupt in
service.

Signed-off-by: Scott Wood <scottwood@freescale.com>
[agraf: remove hunk in code that didn't get applied yet]
Signed-off-by: Alexander Graf <agraf@suse.de>
