m68k: make syscall_trace_enter/leave exist for non-MMU classic m68k types

The assembler entry code calls directly to the syscall_trace_enter() and
syscall_trace_leave() functions. But currently they are conditionaly
compiled out for the non-MMU classic m68k CPU types (so 68328 for example),
resulting in a link error:

      LD      vmlinux
    arch/m68k/platform/68328/built-in.o: In function `do_trace':
    (.text+0x1c): undefined reference to `syscall_trace_enter'
    arch/m68k/platform/68328/built-in.o: In function `do_trace':
    (.text+0x4c): undefined reference to `syscall_trace_leave'

Change the conditional check that includes these functions to be true for
the !defined(CONFIG_MMU) case as well.

Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>