Fix build for !SMP kernels after the Xen MSIX workaround.

Move msix_disable_migration under #ifdef SMP since it doesn't make sense
for !SMP kernels.

PR:		212014
Reported by:	Glyn Grinstead <glyn@grinstead.org>
MFC after:	3 days

sys/amd64/include/intr_machdep.h

@@ -148,8 +148,9 @@ extern cpuset_t intr_cpus;
 #endif
 extern struct mtx icu_lock;
 extern int elcr_found;
-
+#ifdef SMP
 extern int msix_disable_migration;
+#endif
 
 #ifndef DEV_ATPIC
 void	atpic_reset(void);

sys/i386/include/intr_machdep.h

@@ -139,8 +139,9 @@ extern cpuset_t intr_cpus;
 #endif
 extern struct mtx icu_lock;
 extern int elcr_found;
-
+#ifdef SMP
 extern int msix_disable_migration;
+#endif
 
 #ifndef DEV_ATPIC
 void	atpic_reset(void);

sys/x86/x86/msi.c

@@ -149,6 +149,7 @@ struct pic msi_pic = {
 	.pic_reprogram_pin = NULL,
 };
 
+#ifdef SMP
 /**
  * Xen hypervisors prior to 4.6.0 do not properly handle updates to
  * enabled MSI-X table entries.  Allow migration of MSI-X interrupts
@@ -162,6 +163,7 @@ int msix_disable_migration = -1;
 SYSCTL_INT(_machdep, OID_AUTO, disable_msix_migration, CTLFLAG_RDTUN,
     &msix_disable_migration, 0,
     "Disable migration of MSI-X interrupts between CPUs");
+#endif
 
 static int msi_enabled;
 static int msi_last_irq;
@@ -241,8 +243,10 @@ msi_assign_cpu(struct intsrc *isrc, u_int apic_id)
 	if (msi->msi_first != msi)
 		return (EINVAL);
 
+#ifdef SMP
 	if (msix_disable_migration && msi->msi_msix)
 		return (EINVAL);
+#endif
 
 	/* Store information to free existing irq. */
 	old_vector = msi->msi_vector;
@@ -316,10 +320,12 @@ msi_init(void)
 		return;
 	}
 
+#ifdef SMP
 	if (msix_disable_migration == -1) {
 		/* The default is to allow migration of MSI-X interrupts. */
 		msix_disable_migration = 0;
 	}
+#endif
 
 	msi_enabled = 1;
 	intr_register_pic(&msi_pic);

sys/x86/xen/hvm.c

@@ -143,6 +143,7 @@ xen_hvm_init_hypercall_stubs(enum xen_hvm_init_type init_type)
 		printf("XEN: Hypervisor version %d.%d detected.\n", major,
 			minor);
 
+#ifdef SMP
 		if (((major < 4) || (major == 4 && minor <= 5)) &&
 		    msix_disable_migration == -1) {
 			/*
@@ -157,6 +158,7 @@ xen_hvm_init_hypercall_stubs(enum xen_hvm_init_type init_type)
 "Set machdep.msix_disable_migration=0 to forcefully enable it.\n");
 			msix_disable_migration = 1;
 		}
+#endif
 	}
 
 	/*