Move buildroot to bsp directory.

bsp/buildroot/board/acmesystems/arietta-g25/readme.txt

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+Acmesystems Arietta G25
+
+Intro
+=====
+
+This default configuration will allow you to start experimenting with the
+buildroot environment for the Arietta G25. With the current configuration
+it will bring-up the board, and allow access through the serial console.
+
+You can find additional informations, tutorials and a very comprehensive
+documentation on http://www.acmesystems.it/arietta.
+
+Build instructions
+==================
+
+To build an image for the arietta g25 choose the configuration
+corresponding to the arietta variant.
+
+For 128MB RAM variant type:
+
+$ make acmesystems_arietta_g25_128mb_defconfig
+
+else for 256MB RAM variant type:
+
+$ make acmesystems_arietta_g25_256mb_defconfig
+
+then:
+
+$ make
+
+How to write the microSD card
+=============================
+
+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 with "dd":
+
+  $ sudo dd if=output/images/sdcard.img of=/dev/sdX
+
+Insert the microSD card into the arietta slot and power it.
+
+The image just built is fairly basic and the only output
+you will get is on serial console, please consider to use a DPI
+cable (http://www.acmesystems.it/DPI)