x86: allow NODES_SHIFT to be a config option on x86_64

Allow the maximum number of nodes in an x86_64 system to
be configurable. This patch does NOT change the default value
but allows the value to be a config option.
Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/Kconfig

@@ -885,7 +885,7 @@ config NUMA_EMU
 	  number of nodes. This is only useful for debugging.
 
 config NODES_SHIFT
-	int
+	int "Max num nodes shift(1-15)"
 	range 1 15  if X86_64
 	default "6" if X86_64
 	default "4" if X86_NUMAQ