passthrough: don't migrate pirq when it is delivered through VT-d PI

passthrough: don't migrate pirq when it is delivered through VT-d PI

When a vCPU was migrated to another pCPU, pt irqs binded to this vCPU might
also need migration as a optimization to reduce IPI between pCPUs. When VT-d
PI is enabled, interrupt vector will be recorded to a main memory resident
data-structure and a notification whose destination is decided by NDST is
generated. NDST is properly adjusted during vCPU migration so pirq directly
injected to guest needn't be migrated.

This patch adds a indicator, @posted, to show whether the pt irq is delivered
through VT-d PI. Also this patch fixes a bug that hvm_migrate_pirq() accesses
pirq_dpci->gmsi.dest_vcpu_id without checking the pirq_dpci's type.

Signed-off-by: Chao Gao <chao.gao@intel.com>
[jb: remove an extranious check from hvm_migrate_pirq()]
Reviewed-by: Jan Beulich <jbeulich@suse.com>