buildroot: Move to 2016.08 release

Package changes:

 - ethtool: bump to version 4.6
 - dropbear: bump version to 2016.74 (severe security bugfixes)
 - ncurses: various packaging fixes
 - i2c-tools: packaging changes
 - gcc: bump 4.9 series to 4.9.4
 - busybox: bump to version 1.25.0
 - elfutils: bump version to 0.166
 - glibc: bump default to version 2.23
 - eudev: bump version to 3.2. libgudev has moved to it's own package
 - kmod: bump version to 23
 - lvm2: bump version to 2.02.162
 - pciutils: bump to version 3.5.1

Configuration changes:

 - BR2_GLIBC_VERSION_2_23=y is now the default defconfigs that specified
   it do not require it set anymore.

 - The mambo and firenze defconfigs were regenerated to remove redundant
   information. The resulting .config should have no differences.

Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/.gitmodules b/.gitmodules
index 6bda627..4f0f85e 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -1,4 +1,4 @@
 [submodule "buildroot"]
 	path = buildroot
-	branch = 2016.05-op-build
+	branch = 2016.08-op-build
 	url = https://github.com/open-power/buildroot