Bump buidlroot version to 2018.02.6

bsp/buildroot/docs/manual/using-buildroot-toolchain.txt

@@ -9,14 +9,18 @@ can use the toolchain that was generated by Buildroot.
 
 The toolchain generated by Buildroot is located by default in
 +output/host/+. The simplest way to use it is to add
-+output/host/usr/bin/+ to your PATH environment variable and then to
++output/host/bin/+ to your PATH environment variable and then to
 use +ARCH-linux-gcc+, +ARCH-linux-objdump+, +ARCH-linux-ld+, etc.
 
-It is possible to relocate the toolchain - but then +--sysroot+ must
-be passed every time the compiler is called to tell where the
-libraries and header files are.
+It is possible to relocate the toolchain, this allows to distribute
+the toolchain to other developers to build applications for your
+target. To achieve this:
+
+* run +make sdk+, which prepares the toolchain to be relocatable;
+* tarball the contents of the +output/host+ directory;
+* distribute the resulting tarball.
+
+Once the toolchain is installed to the new location, the user must run
+the +relocate-sdk.sh+ script to make sure all paths are updated with
+the new location.
 
-It is also possible to generate the Buildroot toolchain in a directory
-other than +output/host+ by using the +Build options -> Host dir+
-option. This could be useful if the toolchain must be shared with
-other users.