m68k/kernel: Modernize printing of kernel messages

  - Use pr_err_ratelimited() instead of deprecated printk_ratelimit(),
  - Add dummies for validating format strings when debugging is
    disabled,
  - Convert from printk() to pr_*(),
  - Correct printf()-style format specifiers.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>