Add a new interface irq_remapping_cap() to detect whether irq
remapping supports new features, such as VT-d Posted-Interrupts.

Export the function, so that KVM code can check this and use this
mechanism properly.
Signed-off-by: NFeng Wu <feng.wu@intel.com>
Reviewed-by: NJiang Liu <jiang.liu@linux.intel.com>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>
Acked-by: NJoerg Roedel <joro@8bytes.org>
Cc: iommu@lists.linux-foundation.org
Cc: dwmw2@infradead.org
Link: http://lkml.kernel.org/r/1433827237-3382-10-git-send-email-feng.wu@intel.comSigned-off-by: NThomas Gleixner <tglx@linutronix.de>