add .mailmap for proper git-shortlog output

This is the first version of .mailmap created by hand.
Please see "man git-shortlog" for what this commit is trying to do.

Without this file, for example, "git shortlog -n -s" shows as follows:

  2693  Wolfgang Denk     <------
  1002  Stefan Roese      <------
   811  wdenk             <------
   808  Mike Frysinger
   806  Simon Glass
     [snip]
   177  Matthias Fuchs
   154  stroese           <------
   153  Timur Tabi

And then, with this file, it shows as follows:

  3504  Wolfgang Denk     <------
  1156  Stefan Roese      <------
   808  Mike Frysinger
   806  Simon Glass

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Stefan Roese <sr@denx.de>
Cc: Wolfgang Denk <wd@denx.de>