sh: Truncate MAX_ACTIVE_REGIONS for the common case.

Most SH platforms aren't going to need more than a single active
region, ones that need more can pad this out as necessary.
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

arch/sh/mm/Kconfig

@@ -303,6 +303,10 @@ config NODES_SHIFT
 config ARCH_FLATMEM_ENABLE
 	def_bool y
 
+config MAX_ACTIVE_REGIONS
+	int
+	default "1"
+
 config ARCH_POPULATES_NODE_MAP
 	def_bool y