Documentation: update CodingStyle tips for Emacs users

Documentation: update CodingStyle tips for Emacs users

With the previous Emacs tips example the kernel style was made available
for files in the kernel-tree only. This patch updates the tip to add a
separate cc-mode indent style ("linux-tabs-only"). This makes it easy to
switch between different indent styles and also makes the kernel style
easily available for any filetype mode (c++, awk, ...) that is managed
by the Emacs cc-mode.

Signed-off-by: Teemu Likonen <[email protected]>
Signed-off-by: Randy Dunlap <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>