[lantiq] Support booting the Speedport W502V using BRN-BOOT.

[lantiq] Support booting the Speedport W502V using BRN-BOOT.

While the disadvantage is less available flash space, it's easy and
safe to flash without opening the device.
Going back to the original firmware is also possible.

This patch add two firmware utilities, mkbrncmdline and mkbrnboot.

mkbrncmdline patches the uncompressed kernel so the registeres a0 to
a3 are initialized and the memory size is passed in.

mkbrnboot takes the lzma compressed kernel and squashfs images and
creates a firmware image that can be flashed using the BRN-BOOT
recovery kernel, which is booted by holding both buttons when
powering up the device and will listen on http://192.168.2.1.

The firmware file from bin/lantiq/ to use is
openwrt-lantiq-danube-ARV4525PW-BRNDTW502-brnImage

The BRN-BOOT recovery kernel does size-check the image, so if it's
too big to fit into flash it will complain accordingly.

A second patch is needed to make the wired network interface work
since there is no u-boot to pre-initialise it.

Signed-off-by: Tobias Diedrich <ranma+openwrt@tdiedrich.de>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@30532 3c298f89-4303-0410-b956-a3cf2f4a3e73