x2apic/intr-remap: decouple interrupt remapping from x2apic

interrupt remapping must be enabled before enabling x2apic, but
interrupt remapping doesn't depend on x2apic, it can be used
separately. Enable interrupt remapping in init_dmars even x2apic
is not supported.

[dwmw2: Update Kconfig accordingly, fix build with INTR_REMAP && !X2APIC]

Signed-off-by: Weidong Han <weidong.han@intel.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/pci/intel-iommu.c

@@ -1947,6 +1947,15 @@ static int __init init_dmars(void)
 		}
 	}
 
+#ifdef CONFIG_INTR_REMAP
+	if (!intr_remapping_enabled) {
+		ret = enable_intr_remapping(0);
+		if (ret)
+			printk(KERN_ERR
+			       "IOMMU: enable interrupt remapping failed\n");
+	}
+#endif
+
 	/*
 	 * For each rmrr
 	 *   for each dev attached to rmrr