Enable DEVICE_NUMA with up to 8 domains by default on amd64.

8 memory domains should handle a quad-socket board with dual-domain
processors.

Reviewed by:	kib
Relnotes:	maybe?
Differential Revision:	https://reviews.freebsd.org/D5893

sys/amd64/conf/GENERIC

@@ -93,6 +93,7 @@ options 	MALLOC_DEBUG_MAXZONES=8	# Separate malloc(9) zones
 
 # Make an SMP-capable kernel by default
 options 	SMP			# Symmetric MultiProcessor Kernel
+options 	DEVICE_NUMA		# I/O Device Affinity
 
 # CPU frequency control
 device		cpufreq

sys/amd64/conf/MINIMAL

@@ -92,6 +92,7 @@ options 	MALLOC_DEBUG_MAXZONES=8	# Separate malloc(9) zones
 
 # Make an SMP-capable kernel by default
 options 	SMP			# Symmetric MultiProcessor Kernel
+options 	DEVICE_NUMA		# I/O Device Affinity
 
 # CPU frequency control
 device		cpufreq

sys/amd64/include/param.h

@@ -72,7 +72,7 @@
 #endif
 
 #ifndef MAXMEMDOM
-#define	MAXMEMDOM	1
+#define	MAXMEMDOM	8
 #endif
 
 #define	ALIGNBYTES		_ALIGNBYTES