iommu: dmar: Extend struct irte for VT-d Posted-Interrupts

iommu: dmar: Extend struct irte for VT-d Posted-Interrupts

The IRTE (Interrupt Remapping Table Entry) is either an entry for
remapped or for posted interrupts. The hardware distiguishes between
remapped and posted entries by bit 15 in the low 64 bit of the
IRTE. If cleared the entry is remapped, if set it's posted.

The entries have common fields and dependent on the posted bit fields
with different meanings.

Extend struct irte to handle the differences between remap and posted
mode by having three structs in the unions:

        - Shared
        - Remapped
        - Posted

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Feng Wu <feng.wu@intel.com>
Acked-by: Joerg Roedel <joro@8bytes.org>
Cc: jiang.liu@linux.intel.com
Cc: iommu@lists.linux-foundation.org
Cc: dwmw2@infradead.org
Link: http://lkml.kernel.org/r/1433827237-3382-3-git-send-email-feng.wu@intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>