Bump buildroot to 2019.02

bsp/buildroot/board/hardkernel/odroidxu4/readme.txt

@@ -0,0 +1,37 @@
+Odroid XU-4 board with Samsung Exynos 5422 SoC
+
+How to build it
+===============
+
+  $ make odroidxu4_defconfig
+
+Then you can edit the build options using
+
+  $ make menuconfig
+
+Compile all and build rootfs image:
+
+  $ make
+
+Note: you will need to have access to the network, since Buildroot will
+download the packages' sources.
+
+Result of the build
+-------------------
+
+After building, you should obtain all output files in output/images/
+
+
+How to write the SD card or eMMC
+================================
+
+Once the build process is finished you will have an image called "sdcard.img"
+in the output/images/ directory.
+
+Copy the bootable "sdcard.img" onto an SD card or eMMC with "dd":
+
+  $ sudo dd if=output/images/sdcard.img of=/dev/sdX
+
+Insert the SDcard into your ODROID-XU4, and power it up. Your new system
+should come up now.
+