Documentation/kernel-docs.txt: Consistent indenting: 4 spaces

This introduces a consistent indenting of 4 spaces for all
lists.

[mchehab@s-opensource.com: rebased to apply before rename]

Signed-off-by: Richard Sailer <richard@weltraumpflege.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>