Allow the L2X0 outer cache support to be configurable

By default, this option was selected by the platform Kconfig. This
patch adds "depends on" to L2X0 so that it can be enabled/disabled
manually.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm/mm/Kconfig

@@ -701,5 +701,9 @@ config OUTER_CACHE
 	default n
 
 config CACHE_L2X0
-	bool
+	bool "Enable the L2x0 outer cache controller"
+	depends on REALVIEW_EB_ARM11MP || MACH_REALVIEW_PB11MP || MACH_REALVIEW_PB1176
+	default y
 	select OUTER_CACHE
+	help
+	  This option enables the L2x0 PrimeCell.