iommu: dmar: Provide arch specific irq allocation

ia64 and x86 share this driver. x86 is moving to a different irq
allocation and ia64 keeps its private irq_create/destroy stuff.

Use macros to redirect to one or the other. Yes, macros to avoid
include hell.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Grant Likely <grant.likely@linaro.org>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Acked-by: Joerg Roedel <joro@8bytes.org>
Cc: x86@kernel.org
Cc: linux-ia64@vger.kernel.org
Cc: iommu@lists.linux-foundation.org
Link: http://lkml.kernel.org/r/20140507154336.372289825@linutronix.de


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