m68knommu: force setting of CONFIG_CLOCK_FREQ for ColdFire

It is possible to disable the clock selection at configuration time,
but for ColdFire targets we always expect a clock frequency to be
selected. This results in the following compile time error:

  CC      arch/m68k/kernel/asm-offsets.s
In file included from ./arch/m68k/include/asm/timex.h:14:0,
                 from include/linux/timex.h:65,
                 from include/linux/sched.h:19,
                 from arch/m68k/kernel/asm-offsets.c:14:
./arch/m68k/include/asm/coldfire.h:25:2: error: #error "Don't know what your ColdFire CPU clock frequency is??"

Remove CONFIG_CLOCK_SELECT completely and always enable CONFIG_CLOCK_FREQ
for ColdFire.

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