macintosh/via-pmu: Replace via-pmu68k driver with via-pmu driver

Now that the PowerMac via-pmu driver supports m68k PowerBooks,
switch over to that driver and remove the via-pmu68k driver.

Tested-by: Stan Johnson <userm57@yahoo.com>
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>