m68k: do not use m68k startup or interrupt code for ColdFire CPUs

The ColdFire CPUs have their own startup and interrupt code (in the
platform/coldfire directory), and do not use the general m68k startup and
interrupt code. In fact the use of the arch/m68k/kernel/head.o is not about
CONFIG_MMU or not, it is really about the machine type we are compiling for.

Modify the selection and use of head.o to be based on the machine type.
Only select the local ints.o and vectors.o code if we are using the classic
68k CPU types (that use the conventional Morotola MMU or SUN3 MMU).

Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Acked-by: Matt Waddel <mwaddel@yahoo.com>
Acked-by: Kurt Mahan <kmahan@xmission.com>