brcm2708: make it boot on revision 2 raspberry pis

  * update the bootcode.bin to the newest version
    - gpu/cpu mem split is now configured through config.txt, so no need
      to create more than one sd card image (just edit the config.txt)
    - bootcode.bin now supports the never revision 2 raspberry pis

  * add a commented prepopulated config.txt for easier config changes
    Taken from <https://github.com/Evilpaul/RPi-config

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Signed-off-by: Jonas Gorski <jogo@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@36668 3c298f89-4303-0410-b956-a3cf2f4a3e73