KVM: PPC: Rename deliver_interrupts to prepare_to_enter

This function also updates paravirt int_pending, so rename it
to be more obvious that this is a collection of checks run prior
to (re)entering a guest.

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