Bump buildroot to latest 2015.05 base

includes:
- kexec-lite update
- linux 4.2 support

Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>
diff --git a/buildroot b/buildroot
index a75913b..ced5a4d 160000
--- a/buildroot
+++ b/buildroot
@@ -1 +1 @@
-Subproject commit a75913b49a15b8a3f89e816f74329013559a2f43
+Subproject commit ced5a4ded1c37a6a2b0469634ea5e2fff8c3469c