Don't include DMAR map entry zone items in kernel dumps.

Such items may be allocated in the I/O path used by the dumper,
potentially causing the dump to fail. Since there is some precedent
in the DMAR driver for avoiding this problem using _NODUMP, apply
this workaround to the zone as well.

Reported and tested by:	mmacy
Reviewed by:	kib
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D14422

sys/x86/iommu/intel_gas.c

@@ -81,7 +81,7 @@ intel_gas_init(void)
 
 	dmar_map_entry_zone = uma_zcreate("DMAR_MAP_ENTRY",
 	    sizeof(struct dmar_map_entry), NULL, NULL,
-	    NULL, NULL, UMA_ALIGN_PTR, 0);
+	    NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NODUMP);
 }
 SYSINIT(intel_gas, SI_SUB_DRIVERS, SI_ORDER_FIRST, intel_gas_init, NULL);