agp: iommu_gfx_mapped only available if CONFIG_INTEL_IOMMU is set

Kernels with no iommu support cannot ever need the Ironlake
work-around, so never enable it in that case.

Might be better to completely remove the work-around from the kernel
in this case?

Signed-off-by: Keith Packard <keithp@keithp.com>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>

drivers/char/agp/intel-gtt.c

@@ -1186,10 +1186,11 @@ static void gen6_cleanup(void)
 /* Certain Gen5 chipsets require require idling the GPU before
  * unmapping anything from the GTT when VT-d is enabled.
  */
-extern int intel_iommu_gfx_mapped;
 static inline int needs_idle_maps(void)
 {
+#ifdef CONFIG_INTEL_IOMMU
 	const unsigned short gpu_devid = intel_private.pcidev->device;
+	extern int intel_iommu_gfx_mapped;
 
 	/* Query intel_iommu to see if we need the workaround. Presumably that
 	 * was loaded first.
@@ -1198,7 +1199,7 @@ static inline int needs_idle_maps(void)
 	     gpu_devid == PCI_DEVICE_ID_INTEL_IRONLAKE_M_IG) &&
 	     intel_iommu_gfx_mapped)
 		return 1;
-
+#endif
 	return 0;
 }