iommu, x86: Setup Posted-Interrupts capability for Intel iommu

Set Posted-Interrupts capability for Intel iommu when Interrupt
Remapping is enabled, clear it when disabled.

Signed-off-by: Feng Wu <feng.wu@intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
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/1433827237-3382-9-git-send-email-feng.wu@intel.com


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>