a3m071: Add needed dependency on LIB_RAND

Boards using link-local need lib rand.

When link-local is moved to Kconfig, this dependency will be described
there.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/configs/a3m071_defconfig b/configs/a3m071_defconfig
index 1a052e4..c5df596 100644
--- a/configs/a3m071_defconfig
+++ b/configs/a3m071_defconfig
@@ -1,5 +1,6 @@
 CONFIG_PPC=y
+CONFIG_CMD_NET=y
 CONFIG_MPC5xxx=y
 CONFIG_TARGET_A3M071=y
 CONFIG_SPL=y
-CONFIG_CMD_NET=y
+CONFIG_LIB_RAND=y