m68knommu: remove the unused bootlogo.h processing for 68EZ328 and 68VZ328

The 68EZ328 and 68VZ328 platforms currently try to process their bootlogo.h
to make it clean to include in asm files. This is no longer used, the
bootlogo.h file is now included only in C code, so remove all the processing
code in the 68EZ328 and 68VZ328 Makefiles.

Signed-off-by: Greg Ungerer <gerg@uclinux.org>