kvm: remove an atomic on EOI

kvm: remove an atomic on EOI

TMR is set with IRR but does not need to be
cleared on EOI. So we can save an atomic
operation on EOI by checking whether ioapic
needs a specific vector first.

For consistency, don't clear TMR for handled
vectors either: the spec doesn't say that
it needs to be cleared on EOI.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>