We should follow the Linux coding style, which is clearly stated in
the docs/user-guide.mk:

  When making changes to the source for submission to the project,
  the source must be in compliance with the Linux style guide

and Documentation/process/coding-style.rst of Linux Kernel says:

  The limit on the length of lines is 80 columns and this is a
  strongly preferred limit.
     [ snip ]
  However, never break user-visible strings such as printk messages,
  because that breaks the ability to grep for them.

The strings for printf() are user-visible, and can exceed the 80
column limit.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>