intel-iommu: fix build error with INTR_REMAP=y and DMAR=n

dmar.o can be built in the CONFIG_INTR_REMAP=y case but
iommu_calculate_agaw() is only available if VT-d is built as well.

So create an inline version of iommu_calculate_agaw() for the
!CONFIG_DMAR case. The iommu->agaw value wont be used in this
case, but the code is cleaner (has less #ifdefs) if we have it around
unconditionally.
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/dma_remapping.h

@@ -17,7 +17,15 @@ struct dmar_domain;
 struct root_entry;
 
 extern void free_dmar_iommu(struct intel_iommu *iommu);
+
+#ifdef CONFIG_DMAR
 extern int iommu_calculate_agaw(struct intel_iommu *iommu);
+#else
+static inline int iommu_calculate_agaw(struct intel_iommu *iommu)
+{
+	return 0;
+}
+#endif
 
 extern int dmar_disabled;