emacs: Configure gtags mode

- Configure gtags for C-mode.
- Replace cscope keybindings.

Signed-off-by: Ratheesh S <ratheeshreddy@gmail.com>
emacs: fix elisp error for loop

- Fix elisp script error for loop
- Also remove packages dependent on marmalade repo

Signed-off-by: Ratheesh S <ratheeshreddy@gmail.com>