beaglebone: better support for starting and creating images

- Added short readme file with description of first steps how to start.
- Added uEnv.txt so the board can start from SDCard
- Added post-image.sh script to copy included uEnv.txt to output/images

[Peter: strip trailing spaces]
Signed-off-by: Marcin Jabrzyk <marcin.jabrzyk@gmail.com>
Tested-by: Stephan Hoffmann <sho@relinux.de>
Tested-by: Marcin Jabrzyk <marcin.jabrzyk@gmail.com>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

board/beaglebone/post-image.sh

@@ -0,0 +1,6 @@
+#!/bin/sh
+# post-image.sh for BeagleBone
+# 2014, Marcin Jabrzyk <marcin.jabrzyk@gmail.com>
+
+# copy the uEnv.txt to the output/images directory
+cp board/beaglebone/uEnv.txt $BINARIES_DIR/uEnv.txt

board/beaglebone/readme.txt

@@ -0,0 +1,62 @@
+BeagleBone
+
+Intro
+=====
+To be able to use BeagleBone board with the images generated by
+Buildroot, you have prepare the SDCard.
+
+How to build it
+===============
+
+  $ make beaglebone_defconfig
+
+Then you can edit the build options using
+
+  $ make menuconfig
+
+Compile all and build rootfs image:
+
+  $ make
+
+Result of the build
+-------------------
+
+After building, you should get a tree like this:
+
+  output/images/
+  ├── am335x-boneblack.dtb
+  ├── am335x-bone.dtb
+  ├── MLO
+  ├── rootfs.ext2
+  ├── u-boot.img
+  ├── uEnv.txt
+  └── zImage
+
+
+Prepare you SDCard
+==================
+
+You need to prepare first partition in fat32 and marked as bootable,
+and second where you will write rootfs.
+
+Copy the files to boot partition
+
+  $ cp MLO u-boot.img zImage uEnv.txt *.dtb /media/zzzzz
+
+where /media/zzzzz is the mount point
+Then you need to write the rootfs image onto SDCard:
+
+  # dd if=rootfs.ext2 of=/dev/xxxxx
+
+where /dev/xxxxx is the second partition. Use:
+
+  # fdisk -l
+
+to check for correct one.
+
+Finish
+======
+
+Unmount all mounted SDCard partitions and insert the card to BeagleBone.
+Hold the "BOOT" button and apply power. Then release the "BOOT" button.
+The output is available on the serial console.

board/beaglebone/uEnv.txt

@@ -0,0 +1,3 @@
+bootpart=0:1
+bootdir=
+uenvcmd=run loaduimage;run loadramdisk;run findfdt;run loadfdt;run ramboot

configs/beaglebone_defconfig

@@ -8,6 +8,7 @@ BR2_TARGET_GENERIC_HOSTNAME="beaglebone"
 BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_DEVTMPFS=y
 BR2_TARGET_GENERIC_GETTY_PORT="ttyO0"
 # BR2_TARGET_GENERIC_REMOUNT_ROOTFS_RW is not set
+BR2_ROOTFS_POST_IMAGE_SCRIPT="board/beaglebone/post-image.sh"
 
 # filesystem
 BR2_PACKAGE_AM33X_CM3=y