m68k: don't panic if no hardware FPU defined

If we boot up and find no hardware FPU we panic and die.

Change this behavior to be that if we boot up and we _expect_ a hardware
FPU to be present then panic. Don't panic if we don't actually expect to
have any hardware FPU.

This lets us compile a kernel without FPU if we really choose too.

Signed-off-by: Greg Ungerer <gerg@linux-m68k.org>