m68k/sun3: Modernize printing of kernel messages

  - Convert from printk() to pr_*(),
  - Add missing continuations,
  - Do not print nonexistent len variable,
  - Add missing sysname[] variable,
  - Correct printf()-style format specifiers.

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