KVM: PPC: Enable program interrupt to do MMIO

When we get a program interrupt we usually don't expect it to perform an
MMIO operation. But why not? When we emulate paired singles, we can end
up loading or storing to an MMIO address - and the handling of those
happens in the program interrupt handler.

So let's teach the program interrupt handler how to deal with EMULATE_MMIO.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Avi Kivity <avi@redhat.com>