m68k: merge mmu and non-mmu arch Makefiles

Most of the build logic is the same for the mmu and non-mmu m68k targets.
Merge the top level architecture Makefiles back into a single Makefile.

For the most part this is just adding the non-mmu processor types and
their specific cflags and other options into the mmu Makefile.

Note that all the BOARD setting logic that was in the non-mmu Makefile
is completely removed. It was no longer being used at all.

This has been build and run tested on ColdFire targets and ARAnyM.
It has been build tested on all the m68k defconfig targets using a
gcc-4.5.1 based toolchain.

Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Acked-by: Sam Ravnborg <sam@ravnborg.org>