[MIPS] Cleanup ARCH_DISCONTIGMEM_ENABLE and NUMA configuration.

IP27 configuration isn't the only NUMA system - it just happens to be
the currently only supported MIPS NUMA system.  So move the necessary
options back into the main MIPS Kconfig file.
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/Kconfig

@@ -601,6 +601,7 @@ config SGI_IP27
 	select SYS_HAS_CPU_R10000
 	select SYS_SUPPORTS_64BIT_KERNEL
 	select SYS_SUPPORTS_BIG_ENDIAN
+	select SYS_SUPPORTS_NUMA
 	help
 	  This are the SGI Origin 200, Origin 2000 and Onyx 2 Graphics
 	  workstations.  To compile a Linux kernel that runs on these, say Y
@@ -1631,6 +1632,28 @@ config ARCH_FLATMEM_ENABLE
 	def_bool y
 	depends on !NUMA
 
+config ARCH_DISCONTIGMEM_ENABLE
+	bool
+	default y if SGI_IP27
+	help
+	  Say Y to upport efficient handling of discontiguous physical memory,
+	  for architectures which are either NUMA (Non-Uniform Memory Access)
+	  or have huge holes in the physical address space for other reasons.
+	  See <file:Documentation/vm/numa> for more.
+
+config NUMA
+	bool "NUMA Support"
+	depends on SYS_SUPPORTS_NUMA
+	help
+	  Say Y to compile the kernel to support NUMA (Non-Uniform Memory
+	  Access).  This option improves performance on systems with more
+	  than two nodes; on two node systems it is generally better to
+	  leave it disabled; on single node systems disable this option
+	  disabled.
+
+config SYS_SUPPORTS_NUMA
+	bool
+
 config NODES_SHIFT
 	int
 	default "6"

arch/mips/sgi-ip27/Kconfig

@@ -13,23 +13,6 @@ config SGI_SN0_N_MODE
 	  which allows for more memory.  Your system is most probably
 	  running in M-Mode, so you should say N here.
 
-config ARCH_DISCONTIGMEM_ENABLE
-	bool
-	default y if SGI_IP27
-	help
-	  Say Y to upport efficient handling of discontiguous physical memory,
-	  for architectures which are either NUMA (Non-Uniform Memory Access)
-	  or have huge holes in the physical address space for other reasons.
-	  See <file:Documentation/vm/numa> for more.
-
-config NUMA
-	bool "NUMA Support"
-	depends on SGI_IP27
-	help
-	  Say Y to compile the kernel to support NUMA (Non-Uniform Memory
-	  Access).  This option is for configuring high-end multiprocessor
-	  server machines.  If in doubt, say N.
-
 config MAPPED_KERNEL
 	bool "Mapped kernel support"
 	depends on SGI_IP27