buildroot: Update to 2018.02.1

http://lists.busybox.net/pipermail/buildroot/2018-April/218642.html

 > Buildroot 2018.02.1 is a bugfix release on the current long term
 > release, fixing a number of important / security related issues
 > discovered since the 2018.02 release.
 >
 > - Infrastructure: Speed up instrumentation for package size by
 >   comparing timestamps instead of md5 checksums, as doing checksums
 >   could lead to up to 25% longer build time for big configurations.
 >
 > - Add a better fix for build issues for autotools based packages
 >   checking for C++ support on toolchains without C++ support.
 >
 > - Build host-tar if tar is older than 1.27 on the build machine to work
 >   around reproducibility issues with git archives containing long paths.
 >
 > - check-unique-files: Fix for filenames not representable in the users'
 >   locale.
 >
 > - Check-bin-arch: Add support for per-package ignore paths
 >   (<pkg>_BIN_ARCH_EXCLUDE).
 >
 > - linux: Add _NEEDS_HOST_OPENSSL / LIBELF options to ensure these
 >   dependencies are available for Linux configurations needing these
 >   dependencies, similar to how it is done for U-Boot.
 >
 > - linux: Support custom (not in tree) device tree files in addition to
 >   in-tree ones.
 >
 > - Removed unmaintained defconfigs: Creator Ci40, Firefly rk3288,
 >   Freescale mpc8315erdb / p1010rdb_pa, Riotboard, Teliv EVK Pro3.
 >
 > - Security fixes for apache, imagemagick, irssi, libcurl, libopenssl,
 >   libpjsip, libvorbis, memcached, nodejs, ntp, patch, python-webpy,
 >   samba4, tremor, wireshark, xerces
 >
 > - Fixes for download/compilation/runtime issues in busybox, c-ares,
 >   cmake, docker-engine, enlightenment, eudev, fbgrab, freescale-imx,
 >   gtest, intel-microcode, jimtcl, kmod, kodi, ktap, libcoap, libfcgi,
 >   libhttpparser, libminiupnpc, libss7, libssh2, libupnp, libupnpp,
 >   libuv, motion, musl, nodejs, ntp, openblas, opencv3, openocd,
 >   opus-tools, php, pkgconf, postgresql, powerpc-utils,
 >   python-jsonschema, python-webpy, qemu, qt5bsae, qt5script, qt5webkit,
 >   rapidjson, rauc, sam-ba, sngrep, systemd, uboot-tools, uclibc-ng-test,
 >   upmpdcli, xterm, zstd.
 >
 > - New packages: docker-proxy, python-functools32

Full changelog:

 https://git.buildroot.net/buildroot/plain/CHANGES?id=2018.02.1

Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/.gitmodules b/.gitmodules
index 81d08d0..d756b37 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -1,4 +1,4 @@
 [submodule "buildroot"]
 	path = buildroot
-	branch = 2017.11-op-build
+	branch = 2018.02-op-build
 	url = https://github.com/open-power/buildroot