board: stemmy: Copy atags for booting downstream/vendor kernel

board: stemmy: Copy atags for booting downstream/vendor kernel

The U-Boot "stemmy" board is mainly intended to simplify booting
mainline Linux on various smartphones from Samsung based on ST-Ericsson
Ux500. While the mainline kernel is working great, there are still some
features missing there. In particular, it is currently not possible to
charge the battery when using the mainline kernel.

This means that it is still necessary to boot the downstream/vendor
kernel from Samsung sometimes to charge the device. That kernel is
ancient, still uses board files + ATAGS instead of device trees and
relies on a strange very long kernel command line hardcoded in the
Samsung bootloader.

Actually, since mainline is booted with device trees there is a very
simple way to make the old downstream kernel work as well: We can
simply take most of the ATAGS passed to U-Boot from the Samsung
bootloader and copy them as-is when booting a kernel without device
tree. That way the long command line and other needed ATAGS are copied
as-is without having to bother with them.

The only exception is the ATAG_INITRD - since the initrd is loaded
by U-Boot, the atag for that should be generated in U-Boot so it points
to the correct address. All other ATAGS are copied as-is and not
generated in U-Boot.

Also use the chance and provide a serial# for U-Boot by parsing the
ATAG_SERIAL that is also passed by the Samsung bootloader.

Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>