kconfig: require largest userspace memory split

This is needed to maximize userspace entropy on ARM.

Bug: 27796957
Change-Id: I7afe0ff37150aa62a2b7c6ae373dcc44b7f27995
diff --git a/kconfig/arm.config b/kconfig/arm.config
index 12ba109..ba01b5f 100644
--- a/kconfig/arm.config
+++ b/kconfig/arm.config
@@ -19,3 +19,6 @@
 
 # Disallow allocating the first 32k of memory (cannot be 64k due to ARM loader).
 CONFIG_DEFAULT_MMAP_MIN_ADDR=32768
+
+# For maximal userspace memory area (and maximum ASLR).
+CONFIG_VMSPLIT_3G=y