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 <tlikonen@iki.fi>
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/CodingStyle

@@ -483,17 +483,24 @@ values.  To do the latter, you can stick the following in your .emacs file:
     (* (max steps 1)
        c-basic-offset)))
 
+(add-hook 'c-mode-common-hook
+          (lambda ()
+            ;; Add kernel style
+            (c-add-style
+             "linux-tabs-only"
+             '("linux" (c-offsets-alist
+                        (arglist-cont-nonempty
+                         c-lineup-gcc-asm-reg
+                         c-lineup-arglist-tabs-only))))))
+
 (add-hook 'c-mode-hook
           (lambda ()
             (let ((filename (buffer-file-name)))
               ;; Enable kernel mode for the appropriate files
               (when (and filename
                          (string-match "~/src/linux-trees" filename))
                 (setq indent-tabs-mode t)
-                (c-set-style "linux")
-                (c-set-offset 'arglist-cont-nonempty
-                              '(c-lineup-gcc-asm-reg
-                                c-lineup-arglist-tabs-only))))))
+                (c-set-style "linux-tabs-only")))))
 
 This will make emacs go better with the kernel coding style for C
 files below ~/src/linux-trees.