powerpc/40x: Don't enable HCU4 board by default

Fix the HCU4 Kconfig option to 'default n'.  We don't want the
board to always be enabled for other board defconfigs.
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>

arch/powerpc/platforms/40x/Kconfig

@@ -35,7 +35,7 @@ config EP405
 config HCU4
 	bool "Hcu4"
 	depends on 40x
-	default y
+	default n
 	select 405GPR
 	help
 	  This option enables support for the Nestal Maschinen HCU4 board.