bdinfo: m68k: ppc: Move arch-specific code from bdinfo

We don't have an easy way to share these three lines of code with two
architectures. We also want to make it clear that this code is actually
arch-specific.

So just duplicate it in each arch-specific file.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>