Adjust filenames for USB update images on TRAB board.

During an automatic update via USB stick, U-Boot searches for
images with the name "firmware.img" and "kernel.img". This names
are now changed to "firmw_01.img" and "kernl_01.img". This is done,
to prevent updates of new boards (with the new macronics "c" step
flashes) with old, incompatible firmware or kernel versions.
Patch by Martin Krause, 21 Jun 2006