HALFARSED enable toggling promptless kconfig symbols

Some kernel config symbols we need to enable in some configurations
don't have a "prompt" entry in the Kconfig files, meaning that
make oldconfig (or any other make fooconfig) won't change them.
So we add a Kconfig.local where they can be selected

In this patch we hardcode the required symbol. Next step would be
to generalise so that they could be specified in something like a
config.kernel.hiddenConfig attrset

kernel/random.patch

@@ -0,0 +1,9 @@
+diff --git a/Kconfig b/Kconfig
+index 745bc773f567..24a6ea92ee19 100644
+--- a/Kconfig
++++ b/Kconfig
+@@ -30,3 +30,4 @@ source "lib/Kconfig"
+ source "lib/Kconfig.debug"
+ 
+ source "Documentation/Kconfig"
++source "Kconfig.local"