m68k: defconfig: Update defconfigs for v6.12-rc1

  - Enable modular build of the new mul_u64_u64_div_u64() test.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/4092672cb64b86ec3f300b4cf0ea0c2db2b52e2e.1727699197.git.geert@linux-m68k.org