[coreboot] Highlight trailing spaces in our editors (vim, emacs, ..

[Bao, Zheng]

When the trailing spaces are highlighted, it is easy for us to delete it
and don't create new trailing spaces.

Zheng

Vim:
Add following lines in the .vimrc
"""""""""
Highlight ExtraWhitespace ctermfg=DarkGray ctermbg=yellow
" Show trailing whitespace:
:match ExtraWhitespace /\s+$/

Emacs:
Add the following lines into the .emacs
(setq-default show-trailing-whitespace 1)